"The next time we just saved ourselves. I was making some stuff to squirt into filaments for the incandescent lamp. I made about a pound of it. I had used ammonia and bromine. I did not know it at the time, but I had made bromide of nitrogen. I put the large bulk of it in three filters, and after it had been washed and all the water had come through the filter, I opened the three filters and laid them on a hot steam plate to dry with the stuff. While I and Mr. Sadler, one of my assistants, were working near it, there was a sudden flash of light, and a very smart explosion. I said to Sadler: 'What is that?' 'I don't know,' he said, and we paid no attention. In about half a minute there was a sharp concussion, and Sadler said: 'See, it is that stuff on the steam plate.' I grabbed the whole thing and threw it in the sink, and poured water on it. I saved a little of it and found it was a terrific explosive. The reason why those little preliminary explosions took place was that a little had spattered out on the edge of the filter paper, and had dried first and exploded. Had the main body exploded there would have been nothing left of the laboratory I was working in.

"At another time, I had a briquetting machine for briquetting iron ore. I had a lever held down by a powerful spring, and a rod one inch in diameter and four feet long. While I was experimenting with it, and standing beside it, a washer broke, and that spring threw the rod right up to the ceiling with a blast; and it came down again just within an inch of my nose, and went clear through a two-inch plank. That was 'within an inch of your life,' as they say.

"In my experimental plant for concentrating iron ore in the northern part of New Jersey, we had a vertical drier, a column about nine feet square and eighty feet high. At the bottom there was a space where two men could go through a hole; and then all the rest of the column was filled with baffle plates. One day this drier got blocked, and the ore would not run down. So I and the vice-president of the company, Mr. Mallory, crowded through the manhole to see why the ore would not come down. After we got in, the ore did come down and there were fourteen tons of it above us. The men outside knew we were in there, and they had a great time digging us out and getting air to us."

Such incidents brought out in narration the fact that many of the men working with him had been less fortunate, particularly those who had experimented with the Roentgen X-ray, whose ravages, like those of leprosy, were responsible for the mutilation and death of at least one expert assistant. In the early days of work on the incandescent lamp, also, there was considerable trouble with mercury. "I had a series of vacuum-pumps worked by mercury and used for exhausting experimental incandescent lamps. The main pipe, which was full of mercury, was about seven and one-half feet from the floor. Along the length of the pipe were outlets to which thick rubber tubing was connected, each tube to a pump. One day, while experimenting with the mercury pump, my assistant, an awkward country lad from a farm on Staten Island, who had adenoids in his nose and breathed through his mouth, which was always wide open, was looking up at this pipe, at a small leak of mercury, when the rubber tube came off and probably two pounds of mercury went into his mouth and down his throat, and got through his system somehow. In a short time he became salivated, and his teeth got loose. He went home, and shortly his mother appeared at the laboratory with a horsewhip, which she proposed to use on the proprietor. I was fortunately absent, and she was mollified somehow by my other assistants. I had given the boy considerable iodide of potassium to prevent salivation, but it did no good in this case.

"When the first lamp-works were started at Menlo Park, one of my experiments seemed to show that hot mercury gave a better vacuum in the lamp than cold mercury. I thereupon started to heat it. Soon all the men got salivated, and things looked serious; but I found that in the mirror factories, where mercury was used extensively, the French Government made the giving of iodide of potassium compulsory to prevent salivation. I carried out this idea, and made every man take a dose every day, but there was great opposition, and hot mercury was finally abandoned."

It will have been gathered that Edison has owed his special immunity from "occupational diseases" not only to luck but to unusual powers of endurance, and a strong physique, inherited, no doubt, from his father. Mr. Mallory mentions a little fact that bears on this exceptional quality of bodily powers. "I have often been surprised at Edison's wonderful capacity for the instant visual perception of differences in materials that were invisible to others until he would patiently point them out. This had puzzled me for years, but one day I was unexpectedly let into part of the secret. For some little time past Mr. Edison had noticed that he was bothered somewhat in reading print, and I asked him to have an oculist give him reading-glasses. He partially promised, but never took time to attend to it. One day he and I were in the city, and as Mrs. Edison had spoken to me about it, and as we happened to have an hour to spare, I persuaded him to go to an oculist with me. Using no names, I asked the latter to examine the gentleman's eyes. He did so very conscientiously, and it was an interesting experience, for he was kept busy answering Mr. Edison's numerous questions. When the oculist finished, he turned to me and said: 'I have been many years in the business, but have never seen an optic nerve like that of this gentleman. An ordinary optic nerve is about the thickness of a thread, but his is like a cord. He must be a remarkable man in some walk of life. Who is he?'"

It has certainly required great bodily vigor and physical capacity to sustain such fatigue as Edison has all his life imposed upon himself, to the extent on one occasion of going five days without sleep. In a conversation during 1909, he remarked, as though it were nothing out of the way, that up to seven years previously his average of daily working hours was nineteen and one-half, but that since then he figured it at eighteen. He said he stood it easily, because he was interested in everything, and was reading and studying all the time. For instance, he had gone to bed the night before exactly at twelve and had arisen at 4.30 A. M. to read some New York law reports. It was suggested that the secret of it might be that he did not live in the past, but was always looking forward to a greater future, to which he replied: "Yes, that's it. I don't live with the past; I am living for to-day and to-morrow. I am interested in every department of science, arts, and manufacture. I read all the time on astronomy, chemistry, biology, physics, music, metaphysics, mechanics, and other branches—political economy, electricity, and, in fact, all things that are making for progress in the world. I get all the proceedings of the scientific societies, the principal scientific and trade journals, and read them. I also read The Clipper, The Police Gazette, The Billboard, The Dramatic Mirror, and a lot of similar publications, for I like to know what is going on. In this way I keep up to date, and live in a great moving world of my own, and, what's more, I enjoy every minute of it." Referring to some event of the past, he said: "Spilt milk doesn't interest me. I have spilt lots of it, and while I have always felt it for a few days, it is quickly forgotten, and I turn again to the future." During another talk on kindred affairs it was suggested to Edison that, as he had worked so hard all his life, it was about time for him to think somewhat of the pleasures of travel and the social side of life. To which he replied laughingly: "I already have a schedule worked out. From now until I am seventy-five years of age, I expect to keep more or less busy with my regular work, not, however, working as many hours or as hard as I have in the past. At seventy five I expect to wear loud waistcoats with fancy buttons; also gaiter tops; at eighty I expect to learn how to play bridge whist and talk foolishly to the ladies. At eighty-five I expect to wear a full-dress suit every evening at dinner, and at ninety—well, I never plan more than thirty years ahead."

The reference to clothes is interesting, as it is one of the few subjects in which Edison has no interest. It rather bores him. His dress is always of the plainest; in fact, so plain that, at the Bergmann shops in New York, the children attending a parochial Catholic school were wont to salute him with the finger to the head, every time he went by. Upon inquiring, he found that they took him for a priest, with his dark garb, smooth-shaven face, and serious expression. Edison says: "I get a suit that fits me; then I compel the tailors to use that as a jig or pattern or blue-print to make others by. For many years a suit was used as a measurement; once or twice they took fresh measurements, but these didn't fit and they had to go back. I eat to keep my weight constant, hence I need never change measurements." In regard to this, Mr. Mallory furnishes a bit of chat as follows: "In a lawsuit in which I was a witness, I went out to lunch with the lawyers on both sides, and the lawyer who had been cross-examining me stated that he had for a client a Fifth Avenue tailor, who had told him that he had made all of Mr. Edison's clothes for the last twenty years, and that he had never seen him. He said that some twenty years ago a suit was sent to him from Orange, and measurements were made from it, and that every suit since had been made from these measurements. I may add, from my own personal observation, that in Mr. Edison's clothes there is no evidence but that every new suit that he has worn in that time looks as if he had been specially measured for it, which shows how very little he has changed physically in the last twenty years."

Edison has never had any taste for amusements, although he will indulge in the game of "Parchesi" and has a billiard-table in his house. The coming of the automobile was a great boon to him, because it gave him a form of outdoor sport in which he could indulge in a spirit of observation, without the guilty feeling that he was wasting valuable time. In his automobile he has made long tours, and with his family has particularly indulged his taste for botany. That he has had the usual experience in running machines will be evidenced by the following little story from Mr. Mallory: "About three years ago I had a motor-car of a make of which Mr. Edison had already two cars; and when the car was received I made inquiry as to whether any repair parts were carried by any of the various garages in Easton, Pennsylvania, near our cement works. I learned that this particular car was the only one in Easton. Knowing that Mr. Edison had had an experience lasting two or three years with this particular make of car, I determined to ask him for information relative to repair parts; so the next time I was at the laboratory I told him I was unable to get any repair parts in Easton, and that I wished to order some of the most necessary, so that, in case of breakdowns, I would not be compelled to lose the use of the car for several days until the parts came from the automobile factory. I asked his advice as to what I should order, to which he replied: 'I don't think it will be necessary to order an extra top.'" Since that episode, which will probably be appreciated by most automobilists, Edison has taken up the electric automobile, and is now using it as well as developing it. One of the cars equipped with his battery is the Bailey, and Mr. Bee tells the following story in regard to it: "One day Colonel Bailey, of Amesbury, Massachusetts, who was visiting the Automobile Show in New York, came out to the laboratory to see Mr. Edison, as the latter had expressed a desire to talk with him on his next visit to the metropolis. When he arrived at the laboratory, Mr. Edison, who had been up all night experimenting, was asleep on the cot in the library. As a rule we never wake Mr. Edison from sleep, but as he wanted to see Colonel Bailey, who had to go, I felt that an exception should be made, so I went and tapped him on the shoulder. He awoke at once, smiling, jumped up, was instantly himself as usual, and advanced and greeted the visitor. His very first question was: 'Well, Colonel, how did you come out on that experiment?'—referring to some suggestions he had made at their last meeting a year before. For a minute Colonel Bailey did not recall what was referred to; but a few words from Mr. Edison brought it back to his remembrance, and he reported that the results had justified Mr. Edison's expectations."

It might be expected that Edison would have extreme and even radical ideas on the subject of education—and he has, as well as a perfect readiness to express them, because he considers that time is wasted on things that are not essential: "What we need," he has said, "are men capable of doing work. I wouldn't give a penny for the ordinary college graduate, except those from the institutes of technology. Those coming up from the ranks are a darned sight better than the others. They aren't filled up with Latin, philosophy, and the rest of that ninny stuff." A further remark of his is: "What the country needs now is the practical skilled engineer, who is capable of doing everything. In three or four centuries, when the country is settled, and commercialism is diminished, there will be time for the literary men. At present we want engineers, industrial men, good business-like managers, and railroad men." It is hardly to be marvelled at that such views should elicit warm protest, summed up in the comment: "Mr. Edison and many like him see in reverse the course of human progress. Invention does not smooth the way for the practical men and make them possible. There is always too much danger of neglecting thoughts for things, ideas for machinery. No theory of education that aggravates this danger is consistent with national well-being."

Edison is slow to discuss the great mysteries of life, but is of reverential attitude of mind, and ever tolerant of others' beliefs. He is not a religious man in the sense of turning to forms and creeds, but, as might be expected, is inclined as an inventor and creator to argue from the basis of "design" and thence to infer a designer. "After years of watching the processes of nature," he says, "I can no more doubt the existence of an Intelligence that is running things than I do of the existence of myself. Take, for example, the substance water that forms the crystals known as ice. Now, there are hundreds of combinations that form crystals, and every one of them, save ice, sinks in water. Ice, I say, doesn't, and it is rather lucky for us mortals, for if it had done so, we would all be dead. Why? Simply because if ice sank to the bottoms of rivers, lakes, and oceans as fast as it froze, those places would be frozen up and there would be no water left. That is only one example out of thousands that to me prove beyond the possibility of a doubt that some vast Intelligence is governing this and other planets."

A few words as to the domestic and personal side of Edison's life, to which many incidental references have already been made in these pages. He was married in 1873 to Miss Mary Stillwell, who died in 1884, leaving three children—Thomas Alva, William Leslie, and Marion Estelle.

Mr. Edison was married again in 1886 to Miss Mina Miller, daughter of Mr. Lewis Miller, a distinguished pioneer inventor and manufacturer in the field of agricultural machinery, and equally entitled to fame as the father of the "Chautauqua idea," and the founder with Bishop Vincent of the original Chautauqua, which now has so many replicas all over the country, and which started in motion one of the great modern educational and moral forces in America. By this marriage there are three children—Charles, Madeline, and Theodore.

For over a score of years, dating from his marriage to Miss Miller, Edison's happy and perfect domestic life has been spent at Glenmont, a beautiful property acquired at that time in Llewellyn Park, on the higher slopes of Orange Mountain, New Jersey, within easy walking distance of the laboratory at the foot of the hill in West Orange. As noted already, the latter part of each winter is spent at Fort Myers, Florida, where Edison has, on the banks of the Calahoutchie River, a plantation home that is in many ways a miniature copy of the home and laboratory up North. Glenmont is a rather elaborate and florid building in Queen Anne English style, of brick, stone, and wooden beams showing on the exterior, with an abundance of gables and balconies. It is set in an environment of woods and sweeps of lawn, flanked by unusually large conservatories, and always bright in summer with glowing flower beds. It would be difficult to imagine Edison in a stiffly formal house, and this big, cozy, three-story, rambling mansion has an easy freedom about it, without and within, quite in keeping with the genius of the inventor, but revealing at every turn traces of feminine taste and culture. The ground floor, consisting chiefly of broad drawing-rooms, parlors, and dining-hall, is chiefly noteworthy for the "den," or lounging-room, at the end of the main axis, where the family and friends are likely to be found in the evening hours, unless the party has withdrawn for more intimate social intercourse to the interesting and fascinating private library on the floor above. The lounging-room on the ground floor is more or less of an Edison museum, for it is littered with souvenirs from great people, and with mementos of travel, all related to some event or episode. A large cabinet contains awards, decorations, and medals presented to Edison, accumulating in the course of a long career, some of which may be seen in the illustration opposite. Near by may be noticed a bronze replica of the Edison gold medal which was founded in the American Institute of Electrical Engineers, the first award of which was made to Elihu Thomson during the present year (1910). There are statues of serpentine marble, gifts of the late Tsar of Russia, whose admiration is also represented by a gorgeous inlaid and enamelled cigar-case.

There are typical bronze vases from the Society of Engineers of Japan, and a striking desk-set of writing apparatus from Krupp, all the pieces being made out of tiny but massive guns and shells of Krupp steel. In addition to such bric-a-brac and bibelots of all kinds are many pictures and photographs, including the original sketches of the reception given to Edison in 1889 by the Paris Figaro, and a letter from Madame Carnot, placing the Presidential opera-box at the disposal of Mr. and Mrs. Edison. One of the most conspicuous features of the room is a phonograph equipment on which the latest and best productions by the greatest singers and musicians can always be heard, but which Edison himself is everlastingly experimenting with, under the incurable delusion that this domestic retreat is but an extension of his laboratory.

The big library—semi-boudoir—up-stairs is also very expressive of the home life of Edison, but again typical of his nature and disposition, for it is difficult to overlay his many technical books and scientific periodicals with a sufficiently thick crust of popular magazines or current literature to prevent their outcropping into evidence. In like manner the chat and conversation here, however lightly it may begin, turns invariably to large questions and deep problems, especially in the fields of discovery and invention; and Edison, in an easy-chair, will sit through the long evenings till one or two in the morning, pulling meditatively at his eyebrows, quoting something he has just read pertinent to the discussion, hearing and telling new stories with gusto, offering all kinds of ingenious suggestions, and without fail getting hold of pads and sheets of paper on which to make illustrative sketches. He is wonderfully handy with the pencil, and will sometimes amuse himself, while chatting, with making all kinds of fancy bits of penmanship, twisting his signature into circles and squares, but always writing straight lines—so straight they could not be ruled truer. Many a night it is a question of getting Edison to bed, for he would much rather probe a problem than eat or sleep; but at whatever hour the visitor retires or gets up, he is sure to find the master of the house on hand, serene and reposeful, and just as brisk at dawn as when he allowed the conversation to break up at midnight. The ordinary routine of daily family life is of course often interrupted by receptions and parties, visits to the billiard-room, the entertainment of visitors, the departure to and return from college, at vacation periods, of the young people, and matters relating to the many social and philanthropic causes in which Mrs. Edison is actively interested; but, as a matter of fact, Edison's round of toil and relaxation is singularly uniform and free from agitation, and that is the way he would rather have it.

Edison at sixty-three has a fine physique, and being free from serious ailments of any kind, should carry on the traditions of his long-lived ancestors as to a vigorous old age. His hair has whitened, but is still thick and abundant, and though he uses glasses for certain work, his gray-blue eyes are as keen and bright and deeply lustrous as ever, with the direct, searching look in them that they have ever worn. He stands five feet nine and one-half inches high, weighs one hundred and seventy-five pounds, and has not varied as to weight in a quarter of a century, although as a young man he was slim to gauntness. He is very abstemious, hardly ever touching alcohol, caring little for meat, but fond of fruit, and never averse to a strong cup of coffee or a good cigar. He takes extremely little exercise, although his good color and quickness of step would suggest to those who do not know better that he is in the best of training, and one who lives in the open air.

His simplicity as to clothes has already been described. One would be startled to see him with a bright tie, a loud checked suit, or a fancy waistcoat, and yet there is a curious sense of fastidiousness about the plain things he delights in. Perhaps he is not wholly responsible personally for this state of affairs. In conversation Edison is direct, courteous, ready to discuss a topic with anybody worth talking to, and, in spite of his sore deafness, an excellent listener. No one ever goes away from Edison in doubt as to what he thinks or means, but he is ever shy and diffident to a degree if the talk turns on himself rather than on his work.

If the authors were asked, after having written the foregoing pages, to explain here the reason for Edison's success, based upon their observations so far made, they would first answer that he combines with a vigorous and normal physical structure a mind capable of clear and logical thinking, and an imagination of unusual activity. But this would by no means offer a complete explanation. There are many men of equal bodily and mental vigor who have not achieved a tithe of his accomplishment. What other factors are there to be taken into consideration to explain this phenomenon? First, a stolid, almost phlegmatic, nervous system which takes absolutely no notice of ennui—a system like that of a Chinese ivory-carver who works day after day and month after month on a piece of material no larger than your hand. No better illustration of this characteristic can be found than in the development of the nickel pocket for the storage battery, an element the size of a short lead-pencil, on which upward of five years were spent in experiments, costing over a million dollars, day after day, always apparently with the same tubes but with small variations carefully tabulated in the note-books. To an ordinary person the mere sight of such a tube would have been as distasteful, certainly after a week or so, as the smell of a quail to a man striving to eat one every day for a month, near the end of his gastronomic ordeal. But to Edison these small perforated steel tubes held out as much of a fascination at the end of five years as when the search was first begun, and every morning found him as eager to begin the investigation anew as if the battery was an absolutely novel problem to which his thoughts had just been directed.

Another and second characteristic of Edison's personality contributing so strongly to his achievements is an intense, not to say courageous, optimism in which no thought of failure can enter, an optimism born of self-confidence, and becoming—after forty or fifty years of experience more and more a sense of certainty in the accomplishment of success. In the overcoming of difficulties he has the same intellectual pleasure as the chess-master when confronted with a problem requiring all the efforts of his skill and experience to solve. To advance along smooth and pleasant paths, to encounter no obstacles, to wrestle with no difficulties and hardships—such has absolutely no fascination to him. He meets obstruction with the keen delight of a strong man battling with the waves and opposing them in sheer enjoyment, and the greater and more apparently overwhelming the forces that may tend to sweep him back, the more vigorous his own efforts to forge through them. At the conclusion of the ore-milling experiments, when practically his entire fortune was sunk in an enterprise that had to be considered an impossibility, when at the age of fifty he looked back upon five or six years of intense activity expended apparently for naught, when everything seemed most black and the financial clouds were quickly gathering on the horizon, not the slightest idea of repining entered his mind. The main experiment had succeeded—he had accomplished what he sought for. Nature at another point had outstripped him, yet he had broadened his own sum of knowledge to a prodigious extent. It was only during the past summer (1910) that one of the writers spent a Sunday with him riding over the beautiful New Jersey roads in an automobile, Edison in the highest spirits and pointing out with the keenest enjoyment the many beautiful views of valley and wood. The wanderings led to the old ore-milling plant at Edison, now practically a mass of deserted buildings all going to decay. It was a depressing sight, marking such titanic but futile struggles with nature. To Edison, however, no trace of sentiment or regret occurred, and the whole ruins were apparently as much a matter of unconcern as if he were viewing the remains of Pompeii. Sitting on the porch of the White House, where he lived during that period, in the light of the setting sun, his fine face in repose, he looked as placidly over the scene as a happy farmer over a field of ripening corn. All that he said was: "I never felt better in my life than during the five years I worked here. Hard work, nothing to divert my thought, clear air and simple food made my life very pleasant. We learned a great deal. It will be of benefit to some one some time." Similarly, in connection with the storage battery, after having experimented continuously for three years, it was found to fall below his expectations, and its manufacture had to be stopped. Hundreds of thousands of dollars had been spent on the experiments, and, largely without Edison's consent, the battery had been very generally exploited in the press. To stop meant not only to pocket a great loss already incurred, facing a dark and uncertain future, but to most men animated by ordinary human feelings, it meant more than anything else, an injury to personal pride. Pride? Pooh! that had nothing to do with the really serious practical problem, and the writers can testify that at the moment when his decision was reached, work stopped and the long vista ahead was peered into, Edison was as little concerned as if he had concluded that, after all, perhaps peach-pie might be better for present diet than apple-pie. He has often said that time meant very little to him, that he had but a small realization of its passage, and that ten or twenty years were as nothing when considering the development of a vital invention.

These references to personal pride recall another characteristic of Edison wherein he differs from most men. There are many individuals who derive an intense and not improper pleasure in regalia or military garments, with plenty of gold braid and brass buttons, and thus arrayed, in appearing before their friends and neighbors. Putting at the head of the procession the man who makes his appeal to public attention solely because of the brilliancy of his plumage, and passing down the ranks through the multitudes having a gradually decreasing sense of vanity in their personal accomplishment, Edison would be placed at the very end. Reference herein has been made to the fact that one of the two great English universities wished to confer a degree upon him, but that he was unable to leave his work for the brief time necessary to accept the honor. At that occasion it was pointed out to him that he should make every possible sacrifice to go, that the compliment was great, and that but few Americans had been so recognized. It was hopeless—an appeal based on sentiment. Before him was something real—work to be accomplished—a problem to be solved. Beyond, was a prize as intangible as the button of the Legion of Honor, which he concealed from his friends that they might not feel he was "showing off." The fact is that Edison cares little for the approval of the world, but that he cares everything for the approval of himself. Difficult as it may be—perhaps impossible—to trace its origin, Edison possesses what he would probably call a well-developed case of New England conscience, for whose approval he is incessantly occupied.

These, then, may be taken as the characteristics of Edison that have enabled him to accomplish more than most men—a strong body, a clear and active mind, a developed imagination, a capacity of great mental and physical concentration, an iron-clad nervous system that knows no ennui, intense optimism, and courageous self-confidence. Any one having these capacities developed to the same extent, with the same opportunities for use, would probably accomplish as much. And yet there is a peculiarity about him that so far as is known has never been referred to before in print. He seems to be conscientiously afraid of appearing indolent, and in consequence subjects himself regularly to unnecessary hardship. Working all night is seldom necessary, or until two or three o'clock in the morning, yet even now he persists in such tests upon his strength. Recently one of the writers had occasion to present to him a long typewritten document of upward of thirty pages for his approval. It was taken home to Glenmont. Edison had a few minor corrections to make, probably not more than a dozen all told. They could have been embodied by interlineations and marginal notes in the ordinary way, and certainly would not have required more than ten or fifteen minutes of his time. Yet what did he do? HE COPIED OUT PAINSTAKINGLY THE ENTIRE PAPER IN LONG HAND, embodying the corrections as he went along, and presented the result of his work the following morning. At the very least such a task must have occupied several hours. How can such a trait—and scores of similar experiences could be given—be explained except by the fact that, evidently, he felt the need of special schooling in industry—that under no circumstances must he allow a thought of indolence to enter his mind?

Undoubtedly in the days to come Edison will not only be recognized as an intellectual prodigy, but as a prodigy of industry—of hard work. In his field as inventor and man of science he stands as clear-cut and secure as the lighthouse on a rock, and as indifferent to the tumult around. But as the "old man"—and before he was thirty years old he was affectionately so called by his laboratory associates—he is a normal, fun-loving, typical American. His sense of humor is intense, but not of the hothouse, overdeveloped variety. One of his favorite jokes is to enter the legal department with an air of great humility and apply for a job as an inventor! Never is he so preoccupied or fretted with cares as not to drop all thought of his work for a few moments to listen to a new story, with a ready smile all the while, and a hearty, boyish laugh at the end. His laugh, in fact, is sometimes almost aboriginal; slapping his hands delightedly on his knees, he rocks back and forth and fairly shouts his pleasure. Recently a daily report of one of his companies that had just been started contained a large order amounting to several thousand dollars, and was returned by him with a miniature sketch of a small individual viewing that particular item through a telescope! His facility in making hasty but intensely graphic sketches is proverbial. He takes great delight in imitating the lingo of the New York street gamin. A dignified person named James may be greeted with: "Hully Gee! Chimmy, when did youse blow in?" He likes to mimic and imitate types, generally, that are distasteful to him. The sanctimonious hypocrite, the sleek speculator, and others whom he has probably encountered in life are done "to the queen's taste."

One very cold winter's day he entered the laboratory library in fine spirits, "doing" the decayed dandy, with imaginary cane under his arm, struggling to put on a pair of tattered imaginary gloves, with a self-satisfied smirk and leer that would have done credit to a real comedian. This particular bit of acting was heightened by the fact that even in the coldest weather he wears thin summer clothes, generally acid-worn and more or less disreputable. For protection he varies the number of his suits of underclothing, sometimes wearing three or four sets, according to the thermometer.

If one could divorce Edison from the idea of work, and could regard him separate and apart from his embodiment as an inventor and man of science, it might truly be asserted that his temperament is essentially mercurial. Often he is in the highest spirits, with all the spontaneity of youth, and again he is depressed, moody, and violently angry. Anger with him, however, is a good deal like the story attributed to Napoleon:

"Sire, how is it that your judgment is not affected by your great rage?" asked one of his courtiers.

"Because," said the Emperor, "I never allow it to rise above this line," drawing his hand across his throat. Edison has been seen sometimes almost beside himself with anger at a stupid mistake or inexcusable oversight on the part of an assistant, his voice raised to a high pitch, sneeringly expressing his feelings of contempt for the offender; and yet when the culprit, like a bad school-boy, has left the room, Edison has immediately returned to his normal poise, and the incident is a thing of the past. At other times the unsettled condition persists, and his spleen is vented not only on the original instigator but upon others who may have occasion to see him, sometimes hours afterward. When such a fit is on him the word is quickly passed around, and but few of his associates find it necessary to consult with him at the time. The genuine anger can generally be distinguished from the imitation article by those who know him intimately by the fact that when really enraged his forehead between the eyes partakes of a curious rotary movement that cannot be adequately described in words. It is as if the storm-clouds within are moving like a whirling cyclone. As a general rule, Edison does not get genuinely angry at mistakes and other human weaknesses of his subordinates; at best he merely simulates anger. But woe betide the one who has committed an act of bad faith, treachery, dishonesty, or ingratitude; THEN Edison can show what it is for a strong man to get downright mad. But in this respect he is singularly free, and his spells of anger are really few. In fact, those who know him best are continually surprised at his moderation and patience, often when there has been great provocation. People who come in contact with him and who may have occasion to oppose his views, may leave with the impression that he is hot-tempered; nothing could be further from the truth. He argues his point with great vehemence, pounds on the table to emphasize his views, and illustrates his theme with a wealth of apt similes; but, on account of his deafness, it is difficult to make the argument really two-sided. Before the visitor can fully explain his side of the matter some point is brought up that starts Edison off again, and new arguments from his viewpoint are poured forth. This constant interruption is taken by many to mean that Edison has a small opinion of any arguments that oppose him; but he is only intensely in earnest in presenting his own side. If the visitor persists until Edison has seen both sides of the controversy, he is always willing to frankly admit that his own views may be unsound and that his opponent is right. In fact, after such a controversy, both parties going after each other hammer and tongs, the arguments TO HIM being carried on at the very top of one's voice to enable him to hear, and FROM HIM being equally loud in the excitement of the discussion, he has often said: "I see now that my position was absolutely rotten."

Obviously, however, all of these personal characteristics have nothing to do with Edison's position in the world of affairs. They show him to be a plain, easy-going, placid American, with no sense of self-importance, and ready at all times to have his mind turned into a lighter channel. In private life they show him to be a good citizen, a good family man, absolutely moral, temperate in all things, and of great charitableness to all mankind. But what of his position in the age in which he lives? Where does he rank in the mountain range of great Americans?

It is believed that from the other chapters of this book the reader can formulate his own answer to the question.



INTRODUCTION TO THE APPENDIX

THE reader who has followed the foregoing narrative may feel that inasmuch as it is intended to be an historical document, an appropriate addendum thereto would be a digest of all the inventions of Edison. The desirability of such a digest is not to be denied, but as there are some twenty-five hundred or more inventions to be considered (including those covered by caveats), the task of its preparation would be stupendous. Besides, the resultant data would extend this book into several additional volumes, thereby rendering it of value chiefly to the technical student, but taking it beyond the bounds of biography.

We should, however, deem our presentation of Mr. Edison's work to be imperfectly executed if we neglected to include an intelligible exposition of the broader theoretical principles of his more important inventions. In the following Appendix we have therefore endeavored to present a few brief statements regarding Mr. Edison's principal inventions, classified as to subject-matter and explained in language as free from technicalities as is possible. No attempt has been made to conform with strictly scientific terminology, but, for the benefit of the general reader, well-understood conventional expressions, such as "flow of current," etc., have been employed. It should be borne in mind that each of the following items has been treated as a whole or class, generally speaking, and not as a digest of all the individual patents relating to it. Any one who is sufficiently interested can obtain copies of any of the patents referred to for five cents each by addressing the Commissioner of Patents, Washington, D. C.



APPENDIX



I. THE STOCK PRINTER

IN these modern days, when the Stock Ticker is in universal use, one seldom, if ever, hears the name of Edison coupled with the little instrument whose chatterings have such tremendous import to the whole world. It is of much interest, however, to remember the fact that it was by reason of his notable work in connection with this device that he first became known as an inventor. Indeed, it was through the intrinsic merits of his improvements in stock tickers that he made his real entree into commercial life.

The idea of the ticker did not originate with Edison, as we have already seen in Chapter VII of the preceding narrative, but at the time of his employment with the Western Union, in Boston, in 1868, the crudities of the earlier forms made an impression on his practical mind, and he got out an improved instrument of his own, which he introduced in Boston through the aid of a professional promoter. Edison, then only twenty-one, had less business experience than the promoter, through whose manipulation he soon lost his financial interest in this early ticker enterprise. The narrative tells of his coming to New York in 1869, and immediately plunging into the business of gold and stock reporting. It was at this period that his real work on stock printers commenced, first individually, and later as a co-worker with F. L. Pope. This inventive period extended over a number of years, during which time he took out forty-six patents on stock-printing instruments and devices, two of such patents being issued to Edison and Pope as joint inventors. These various inventions were mostly in the line of development of the art as it progressed during those early years, but out of it all came the Edison universal printer, which entered into very extensive use, and which is still used throughout the United States and in some foreign countries to a considerable extent at this very day.

Edison's inventive work on stock printers has left its mark upon the art as it exists at the present time. In his earlier work he directed his attention to the employment of a single-circuit system, in which only one wire was required, the two operations of setting the type-wheels and of printing being controlled by separate electromagnets which were actuated through polarized relays, as occasion required, one polarity energizing the electromagnet controlling the type-wheels, and the opposite polarity energizing the electromagnet controlling the printing. Later on, however, he changed over to a two-wire circuit, such as shown in Fig. 2 of this article in connection with the universal stock printer. In the earliest days of the stock printer, Edison realized the vital commercial importance of having all instruments recording precisely alike at the same moment, and it was he who first devised (in 1869) the "unison stop," by means of which all connected instruments could at any moment be brought to zero from the central transmitting station, and thus be made to work in correspondence with the central instrument and with one another. He also originated the idea of using only one inking-pad and shifting it from side to side to ink the type-wheels. It was also in Edison's stock printer that the principle of shifting type-wheels was first employed. Hence it will be seen that, as in many other arts, he made a lasting impression in this one by the intrinsic merits of the improvements resulting from his work therein.

We shall not attempt to digest the forty-six patents above named, nor to follow Edison through the progressive steps which led to the completion of his universal printer, but shall simply present a sketch of the instrument itself, and follow with a very brief and general explanation of its theory. The Edison universal printer, as it virtually appears in practice, is illustrated in Fig. 1 below, from which it will be seen that the most prominent parts are the two type-wheels, the inking-pad, and the paper tape feeding from the reel, all appropriately placed in a substantial framework.

The electromagnets and other actuating mechanism cannot be seen plainly in this figure, but are produced diagrammatically in Fig. 2, and somewhat enlarged for convenience of explanation.

It will be seen that there are two electromagnets, one of which, TM, is known as the "type-magnet," and the other, PM, as the "press-magnet," the former having to do with the operation of the type-wheels, and the latter with the pressing of the paper tape against them. As will be seen from the diagram, the armature, A, of the type-magnet has an extension arm, on the end of which is an escapement engaging with a toothed wheel placed at the extremity of the shaft carrying the type-wheels. This extension arm is pivoted at B. Hence, as the armature is alternately attracted when current passes around its electromagnet, and drawn up by the spring on cessation of current, it moves up and down, thus actuating the escapement and causing a rotation of the toothed wheel in the direction of the arrow. This, in turn, brings any desired letters or figures on the type-wheels to a central point, where they may be impressed upon the paper tape. One type-wheel carries letters, and the other one figures. These two wheels are mounted rigidly on a sleeve carried by the wheel-shaft. As it is desired to print from only one type-wheel at a time, it becomes necessary to shift them back and forth from time to time, in order to bring the desired characters in line with the paper tape. This is accomplished through the movements of a three-arm rocking-lever attached to the wheel-sleeve at the end of the shaft. This lever is actuated through the agency of two small pins carried by an arm projecting from the press-lever, PL. As the latter moves up and down the pins play upon the under side of the lower arm of the rocking-lever, thus canting it and pushing the type-wheels to the right or left, as the case may be. The operation of shifting the type-wheels will be given further on.

The press-lever is actuated by the press-magnet. From the diagram it will be seen that the armature of the latter has a long, pivoted extension arm, or platen, trough-like in shape, in which the paper tape runs. It has already been noted that the object of the press-lever is to press this tape against that character of the type-wheel centrally located above it at the moment. It will at once be perceived that this action takes place when current flows through the electromagnet and its armature is attracted downward, the platen again dropping away from the type-wheel as the armature is released upon cessation of current. The paper "feed" is shown at the end of the press-lever, and consists of a push "dog," or pawl, which operates to urge the paper forward as the press-lever descends.

The worm-gear which appears in the diagram on the shaft, near the toothed wheel, forms part of the unison stop above referred to, but this device is not shown in full, in order to avoid unnecessary complications of the drawing.

At the right-hand side of the diagram (Fig. 2) is shown a portion of the transmitting apparatus at a central office. Generally speaking, this consists of a motor-driven cylinder having metallic pins placed at intervals, and arranged spirally, around its periphery. These pins correspond in number to the characters on the type-wheels. A keyboard (not shown) is arranged above the cylinder, having keys lettered and numbered corresponding to the letters and figures on the type-wheels. Upon depressing any one of these keys the motion of the cylinder is arrested when one of its pins is caught and held by the depressed key. When the key is released the cylinder continues in motion. Hence, it is evident that the revolution of the cylinder may be interrupted as often as desired by manipulation of the various keys in transmitting the letters and figures which are to be recorded by the printing instrument. The method of transmission will presently appear.

In the sketch (Fig. 2) there will be seen, mounted upon the cylinder shaft, two wheels made up of metallic segments insulated from each other, and upon the hubs of these wheels are two brushes which connect with the main battery. Resting upon the periphery of these two segmental wheels there are two brushes to which are connected the wires which carry the battery current to the type-magnet and press-magnet, respectively, as the brushes make circuit by coming in contact with the metallic segments. It will be remembered that upon the cylinder there are as many pins as there are characters on the type-wheels of the ticker, and one of the segmental wheels, W, has a like number of metallic segments, while upon the other wheel, W', there are only one-half that number. The wheel W controls the supply of current to the press-magnet, and the wheel W' to the type-magnet. The type-magnet advances the letter and figure wheels one step when the magnet is energized, and a succeeding step when the circuit is broken. Hence, the metallic contact surfaces on wheel W' are, as stated, only half as many as on the wheel W, which controls the press-magnet.

It should be borne in mind, however, that the contact surfaces and insulated surfaces on wheel W' are together equal in number to the characters on the type-wheels, but the retractile spring of TM does half the work of operating the escapement. On the other hand, the wheel W has the full number of contact surfaces, because it must provide for the operative closure of the press-magnet circuit whether the brush B' is in engagement with a metallic segment or an insulated segment of the wheel W'. As the cylinder revolves, the wheels are carried around with its shaft and current impulses flow through the wires to the magnets as the brushes make contact with the metallic segments of these wheels.

One example will be sufficient to convey to the reader an idea of the operation of the apparatus. Assuming, for instance, that it is desired to send out the letters AM to the printer, let us suppose that the pin corresponding to the letter A is at one end of the cylinder and near the upper part of its periphery, and that the letter M is about the centre of the cylinder and near the lower part of its periphery. The operator at the keyboard would depress the letter A, whereupon the cylinder would in its revolution bring the first-named pin against the key. During the rotation of the cylinder a current would pass through wheel W' and actuate TM, drawing down the armature and operating the escapement, which would bring the type-wheel to a point where the letter A would be central as regards the paper tape When the cylinder came to rest, current would flow through the brush of wheel W to PM, and its armature would be attracted, causing the platen to be lifted and thus bringing the paper tape in contact with the type-wheel and printing the letter A. The operator next sends the letter M by depressing the appropriate key. On account of the position of the corresponding pin, the cylinder would make nearly half a revolution before bringing the pin to the key. During this half revolution the segmental wheels have also been turning, and the brushes have transmitted a number of current impulses to TM, which have caused it to operate the escapement a corresponding number of times, thus turning the type-wheels around to the letter M. When the cylinder stops, current once more goes to the press-magnet, and the operation of lifting and printing is repeated. As a matter of fact, current flows over both circuits as the cylinder is rotated, but the press-magnet is purposely made to be comparatively "sluggish" and the narrowness of the segments on wheel W tends to diminish the flow of current in the press circuit until the cylinder comes to rest, when the current continuously flows over that circuit without interruption and fully energizes the press-magnet. The shifting of the type-wheels is brought about as follows: On the keyboard of the transmitter there are two characters known as "dots"—namely, the letter dot and the figure dot. If the operator presses one of these dot keys, it is engaged by an appropriate pin on the revolving cylinder. Meanwhile the type-wheels are rotating, carrying with them the rocking-lever, and current is pulsating over both circuits. When the type-wheels have arrived at the proper point the rocking-lever has been carried to a position where its lower arm is directly over one of the pins on the arm extending from the platen of the press-lever. The cylinder stops, and current operates the sluggish press-magnet, causing its armature to be attracted, thus lifting the platen and its projecting arm. As the arm lifts upward, the pin moves along the under side of the lower arm of the rocking-lever, thus causing it to cant and shift the type-wheels to the right or left, as desired. The principles of operation of this apparatus have been confined to a very brief and general description, but it is believed to be sufficient for the scope of this article.

NOTE.—The illustrations in this article are reproduced from American Telegraphy and Encyclopedia of the Telegraph, by William Maver, Jr., by permission of Maver Publishing Company, New York.



II. THE QUADRUPLEX AND PHONOPLEX

EDISON'S work in stock printers and telegraphy had marked him as a rising man in the electrical art of the period but his invention of quadruplex telegraphy in 1874 was what brought him very prominently before the notice of the public. Duplex telegraphy, or the sending of two separate messages in opposite directions at the same time over one line was known and practiced previous to this time, but quadruplex telegraphy, or the simultaneous sending of four separate messages, two in each direction, over a single line had not been successfully accomplished, although it had been the subject of many an inventor's dream and the object of anxious efforts for many long years.

In the early part of 1873, and for some time afterward, the system invented by Joseph Stearns was the duplex in practical use. In April of that year, however, Edison took up the study of the subject and filed two applications for patents. One of these applications [23] embraced an invention by which two messages could be sent not only duplex, or in opposite directions as above explained, but could also be sent "diplex"—that is to say, in one direction, simultaneously, as separate and distinct messages, over the one line. Thus there was introduced a new feature into the art of multiplex telegraphy, for, whereas duplexing (accomplished by varying the strength of the current) permitted messages to be sent simultaneously from opposite stations, diplexing (achieved by also varying the direction of the current) permitted the simultaneous transmission of two messages from the same station and their separate reception at the distant station.

[Footnote 23: Afterward issued as Patent No. 162,633, April 27, 1875.]

The quadruplex was the tempting goal toward which Edison now constantly turned, and after more than a year's strenuous work he filed a number of applications for patents in the late summer of 1874. Among them was one which was issued some years afterward as Patent No. 480,567, covering his well-known quadruplex. He had improved his own diplex, combined it with the Stearns duplex and thereby produced a system by means of which four messages could be sent over a single line at the same time, two in each direction.

As the reader will probably be interested to learn something of the theoretical principles of this fascinating invention, we shall endeavor to offer a brief and condensed explanation thereof with as little technicality as the subject will permit. This explanation will necessarily be of somewhat elementary character for the benefit of the lay reader, whose indulgence is asked for an occasional reiteration introduced for the sake of clearness of comprehension. While the apparatus and the circuits are seemingly very intricate, the principles are really quite simple, and the difficulty of comprehension is more apparent than real if the underlying phenomena are studied attentively.

At the root of all systems of telegraphy, including multiplex systems, there lies the single basic principle upon which their performance depends—namely, the obtaining of a slight mechanical movement at the more or less distant end of a telegraph line. This is accomplished through the utilization of the phenomena of electromagnetism. These phenomena are easy of comprehension and demonstration. If a rod of soft iron be wound around with a number of turns of insulated wire, and a current of electricity be sent through the wire, the rod will be instantly magnetized and will remain a magnet as long as the current flows; but when the current is cut off the magnetic effect instantly ceases. This device is known as an electromagnet, and the charging and discharging of such a magnet may, of course, be repeated indefinitely. Inasmuch as a magnet has the power of attracting to itself pieces of iron or steel, the basic importance of an electromagnet in telegraphy will be at once apparent when we consider the sounder, whose clicks are familiar to every ear. This instrument consists essentially of an electro-magnet of horseshoe form with its two poles close together, and with its armature, a bar of iron, maintained in close proximity to the poles, but kept normally in a retracted position by a spring. When the distant operator presses down his key the circuit is closed and a current passes along the line and through the (generally two) coils of the electromagnet, thus magnetizing the iron core. Its attractive power draws the armature toward the poles. When the operator releases the pressure on his key the circuit is broken, current does not flow, the magnetic effect ceases, and the armature is drawn back by its spring. These movements give rise to the clicking sounds which represent the dots and dashes of the Morse or other alphabet as transmitted by the operator. Similar movements, produced in like manner, are availed of in another instrument known as the relay, whose office is to act practically as an automatic transmitter key, repeating the messages received in its coils, and sending them on to the next section of the line, equipped with its own battery; or, when the message is intended for its own station, sending the message to an adjacent sounder included in a local battery circuit. With a simple circuit, therefore, between two stations and where an intermediate battery is not necessary, a relay is not used.

Passing on to the consideration of another phase of the phenomena of electromagnetism, the reader's attention is called to Fig. 1, in which will be seen on the left a simple form of electromagnet consisting of a bar of soft iron wound around with insulated wire, through which a current is flowing from a battery. The arrows indicate the direction of flow.

All magnets have two poles, north and south. A permanent magnet (made of steel, which, as distinguished from soft iron, retains its magnetism for long periods) is so called because it is permanently magnetized and its polarity remains fixed. In an electromagnet the magnetism exists only as long as current is flowing through the wire, and the polarity of the soft-iron bar is determined by the DIRECTION of flow of current around it for the time being. If the direction is reversed, the polarity will also be reversed. Assuming, for instance, the bar to be end-on toward the observer, that end will be a south pole if the current is flowing from left to right, clockwise, around the bar; or a north pole if flowing in the other direction, as illustrated at the right of the figure. It is immaterial which way the wire is wound around the bar, the determining factor of polarity being the DIRECTION of the current. It will be clear, therefore, that if two EQUAL currents be passed around a bar in opposite directions (Fig. 3) they will tend to produce exactly opposite polarities and thus neutralize each other. Hence, the bar would remain non-magnetic.

As the path to the quadruplex passes through the duplex, let us consider the Stearns system, after noting one other principle—namely, that if more than one path is presented in which an electric current may complete its circuit, it divides in proportion to the resistance of each path. Hence, if we connect one pole of a battery with the earth, and from the other pole run to the earth two wires of equal resistance as illustrated in Fig. 2, equal currents will traverse the wires.

The above principles were employed in the Stearns differential duplex system in the following manner: Referring to Fig. 3, suppose a wire, A, is led from a battery around a bar of soft iron from left to right, and another wire of equal resistance and equal number of turns, B, around from right to left. The flow of current will cause two equal opposing actions to be set up in the bar; one will exactly offset the other, and no magnetic effect will be produced. A relay thus wound is known as a differential relay—more generally called a neutral relay.

The non-technical reader may wonder what use can possibly be made of an apparently non-operative piece of apparatus. It must be borne in mind, however, in considering a duplex system, that a differential relay is used AT EACH END of the line and forms part of the circuit; and that while each relay must be absolutely unresponsive to the signals SENT OUT FROM ITS HOME OFFICE, it must respond to signals transmitted by a DISTANT OFFICE. Hence, the next figure (4), with its accompanying explanation, will probably make the matter clear. If another battery, D, be introduced at the distant end of the wire A the differential or neutral relay becomes actively operative as follows: Battery C supplies wires A and B with an equal current, but battery D doubles the strength of the current traversing wire A. This is sufficient to not only neutralize the magnetism which the current in wire B would tend to set up, but also—by reason of the excess of current in wire A—to make the bar a magnet whose polarity would be determined by the direction of the flow of current around it.

In the arrangement shown in Fig. 4 the batteries are so connected that current flow is in the same direction, thus doubling the amount of current flowing through wire A. But suppose the batteries were so connected that the current from each set flowed in an opposite direction? The result would be that these currents would oppose and neutralize each other, and, therefore, none would flow in wire A. Inasmuch, however, as there is nothing to hinder, current would flow from battery C through wire B, and the bar would therefore be magnetized. Hence, assuming that the relay is to be actuated from the distant end, D, it is in a sense immaterial whether the batteries connected with wire A assist or oppose each other, as, in either case, the bar would be magnetized only through the operation of the distant key.

A slight elaboration of Fig. 4 will further illustrate the principle of the differential duplex. In Fig. 5 are two stations, A the home end, and B the distant station to which a message is to be sent. The relay at each end has two coils, 1 and 2, No. 1 in each case being known as the "main-line coil" and 2 as the "artificial-line coil." The latter, in each case, has in its circuit a resistance, R, to compensate for the resistance of the main line, so that there shall be no inequalities in the circuits. The artificial line, as well as that to which the two coils are joined, are connected to earth. There is a battery, C, and a key, K. When the key is depressed, current flows through the relay coils at A, but no magnetism is produced, as they oppose each other. The current, however, flows out through the main-line coil over the line and through the main-line coil 1 at B, completing its circuit to earth and magnetizing the bar of the relay, thus causing its armature to be attracted. On releasing the key the circuit is broken and magnetism instantly ceases.

It will be evident, therefore, that the operator at A may cause the relay at B to act without affecting his own relay. Similar effects would be produced from B to A if the battery and key were placed at the B end.

If, therefore, like instruments are placed at each end of the line, as in Fig. 6, we have a differential duplex arrangement by means of which two operators may actuate relays at the ends distant from them, without causing the operation of the relays at their home ends. In practice this is done by means of a special instrument known as a continuity preserving transmitter, or, usually, as a transmitter. This consists of an electromagnet, T, operated by a key, K, and separate battery. The armature lever, L, is long, pivoted in the centre, and is bent over at the end. At a point a little beyond its centre is a small piece of insulating material to which is screwed a strip of spring metal, S. Conveniently placed with reference to the end of the lever is a bent metallic piece, P, having a contact screw in its upper horizontal arm, and attached to the lower end of this bent piece is a post, or standard, to which the main battery is electrically connected. The relay coils are connected by wire to the spring piece, S, and the armature lever is connected to earth. If the key is depressed, the armature is attracted and its bent end is moved upward, depressing the spring which makes contact with the upper screw, which places the battery to the line, and simultaneously breaks the ground connection between the spring and the upturned end of the lever, as shown at the left. When the key is released the battery is again connected to earth. The compensating resistances and condensers necessary for a duplex arrangement are shown in the diagram.

In Fig. 6 one transmitter is shown as closed, at A, while the other one is open. From our previous illustrations and explanations it will be readily seen that, with the transmitter closed at station A, current flows via post P, through S, and to both relay coils at A, thence over the main line to main-line coil at B, and down to earth through S and the armature lever with its grounded wire. The relay at A would be unresponsive, but the core of the relay at B would be magnetized and its armature respond to signals from A. In like manner, if the transmitter at B be closed, current would flow through similar parts and thus cause the relay at A to respond. If both transmitters be closed simultaneously, both batteries will be placed to the line, which would practically result in doubling the current in each of the main-line coils, in consequence of which both relays are energized and their armatures attracted through the operation of the keys at the distant ends. Hence, two messages can be sent in opposite directions over the same line simultaneously.

The reader will undoubtedly see quite clearly from the above system, which rests upon varying the STRENGTH of the current, that two messages could not be sent in the same direction over the one line at the same time. To accomplish this object Edison introduced another and distinct feature—namely, the using of the same current, but ALSO varying its DIRECTION of flow; that is to say, alternately reversing the POLARITY of the batteries as applied to the line and thus producing corresponding changes in the polarity of another specially constructed type of relay, called a polarized relay. To afford the reader a clear conception of such a relay we would refer again to Fig. 1 and its explanation, from which it appears that the polarity of a soft-iron bar is determined not by the strength of the current flowing around it but by the direction thereof.

With this idea clearly in mind, the theory of the polarized relay, generally called "polar" relay, as presented in the diagram (Fig. 7), will be readily understood.

A is a bar of soft iron, bent as shown, and wound around with insulated copper wire, the ends of which are connected with a battery, B, thus forming an electromagnet. An essential part of this relay consists of a swinging PERMANENT magnet, C, whose polarity remains fixed, that end between the terminals of the electromagnet being a north pole. Inasmuch as unlike poles of magnets are attracted to each other and like poles repelled, it follows that this north pole will be repelled by the north pole of the electromagnet, but will swing over and be attracted by its south pole. If the direction of flow of current be reversed, by reversing the battery, the electromagnetic polarity also reverses and the end of the permanent magnet swings over to the other side. This is shown in the two figures of Fig. 7. This device being a relay, its purpose is to repeat transmitted signals into a local circuit, as before explained. For this purpose there are provided at D and E a contact and a back stop, the former of which is opened and closed by the swinging permanent magnet, thus opening and closing the local circuit.

Manifestly there must be provided some convenient way for rapidly transposing the direction of the current flow if such a device as the polar relay is to be used for the reception of telegraph messages, and this is accomplished by means of an instrument called a pole-changer, which consists essentially of a movable contact piece connected permanently to the earth, or grounded, and arranged to connect one or the other pole of a battery to the line and simultaneously ground the other pole. This action of the pole-changer is effected by movements of the armature of an electromagnet through the manipulation of an ordinary telegraph key by an operator at the home station, as in the operation of the "transmitter," above referred to.

By a combination of the neutral relay and the polar relay two operators, by manipulating two telegraph keys in the ordinary way, can simultaneously send two messages over one line in the SAME direction with the SAME current, one operator varying its strength and the other operator varying its polarity or direction of flow. This principle was covered by Edison's Patent No. 162,633, and was known as the "diplex" system, although, in the patent referred to, Edison showed and claimed the adaptation of the principle to duplex telegraphy. Indeed, as a matter of fact, it was found that by winding the polar relay differentially and arranging the circuits and collateral appliances appropriately, the polar duplex system was more highly efficient than the neutral system, and it is extensively used to the present day.

Thus far we have referred to two systems, one the neutral or differential duplex, and the other the combination of the neutral and polar relays, making a diplex system. By one of these two systems a single wire could be used for sending two messages in opposite directions, and by the other in the same direction or in opposite directions. Edison followed up his work on the diplex and combined the two systems into the quadruplex, by means of which FOUR messages could be sent and received simultaneously over the one wire, two in each direction, thus employing eight operators—four at each end—two sending and two receiving. The general principles of quadruplex telegraphy are based upon the phenomena which we have briefly outlined in connection with the neutral relay and the polar relay. The equipment of such a system at each end of the line consists of these two instruments, together with the special form of transmitter and the pole-changer and their keys for actuating the neutral and polar relays at the other, or distant, end. Besides these there are the compensating resistances and condensers. All of these will be seen in the diagram (Fig. 8). It will be understood, of course, that the polar relay, as used in the quadruplex system, is wound differentially, and therefore its operation is somewhat similar in principle to that of the differentially wound neutral relay, in that it does not respond to the operation of the key at the home office, but only operates in response to the movements of the distant key.

Our explanation has merely aimed to show the underlying phenomena and principles in broad outline without entering into more detail than was deemed absolutely necessary. It should be stated, however, that between the outline and the filling in of the details there was an enormous amount of hard work, study, patient plodding, and endless experiments before Edison finally perfected his quadruplex system in the year 1874.

If it were attempted to offer here a detailed explanation of the varied and numerous operations of the quadruplex, this article would assume the proportions of a treatise. An idea of their complexity may be gathered from the following, which is quoted from American Telegraphy and Encyclopedia of the Telegraph, by William Maver, Jr.:

"It may well be doubted whether in the whole range of applied electricity there occur such beautiful combinations, so quickly made, broken up, and others reformed, as in the operation of the Edison quadruplex. For example, it is quite demonstrable that during the making of a simple dash of the Morse alphabet by the neutral relay at the home station the distant pole-changer may reverse its battery several times; the home pole-changer may do likewise, and the home transmitter may increase and decrease the electromotive force of the home battery repeatedly. Simultaneously, and, of course, as a consequence of the foregoing actions, the home neutral relay itself may have had its magnetism reversed several times, and the SIGNAL, that is, the dash, will have been made, partly by the home battery, partly by the distant and home batteries combined, partly by current on the main line, partly by current on the artificial line, partly by the main-line 'static' current, partly by the condenser static current, and yet, on a well-adjusted circuit the dash will have been produced on the quadruplex sounder as clearly as any dash on an ordinary single-wire sounder."

We present a diagrammatic illustration of the Edison quadruplex, battery key system, in Fig. 8, and refer the reader to the above or other text-books if he desires to make a close study of its intricate operations. Before finally dismissing the quadruplex, and for the benefit of the inquiring reader who may vainly puzzle over the intricacies of the circuits shown in Fig. 8, a hint as to an essential difference between the neutral relay, as used in the duplex and as used in the quadruplex, may be given. With the duplex, as we have seen, the current on the main line is changed in strength only when both keys at OPPOSITE stations are closed together, so that a current due to both batteries flows over the main line. When a single message is sent from one station to the other, or when both stations are sending messages that do not conflict, only one battery or the other is connected to the main line; but with the quadruplex, suppose one of the operators, in New York for instance, is sending reversals of current to Chicago; we can readily see how these changes in polarity will operate the polar relay at the distant station, but why will they not also operate the neutral relay at the distant station as well? This difficulty was solved by dividing the battery at each station into two unequal parts, the smaller battery being always in circuit with the pole-changer ready to have its polarity reversed on the main line to operate the distant polar relay, but the spring retracting the armature of the neutral relay is made so stiff as to resist these weak currents. If, however, the transmitter is operated at the same end, the entire battery is connected to the main line, and the strength of this current is sufficient to operate the neutral relay. Whether the part or all the battery is alternately connected to or disconnected from the main line by the transmitter, the current so varied in strength is subject to reversal of polarity by the pole-changer; but the variations in strength have no effect upon the distant polar relay, because that relay being responsive to changes in polarity of a weak current is obviously responsive to corresponding changes in polarity of a powerful current. With this distinction before him, the reader will have no difficulty in following the circuits of Fig. 8, bearing always in mind that by reason of the differential winding of the polar and neutral relays, neither of the relays at one station will respond to the home battery, and can only respond to the distant battery—the polar relay responding when the polarity of the current is reversed, whether the current be strong or weak, and the neutral relay responding when the line-current is increased, regardless of its polarity. It should be added that besides the system illustrated in Fig. 8, which is known as the differential principle, the quadruplex was also arranged to operate on the Wheatstone bridge principle; but it is not deemed necessary to enter into its details. The underlying phenomena were similar, the difference consisting largely in the arrangement of the circuits and apparatus. [24]

[Footnote 24: Many of the illustrations in this article are reproduced from American Telegraphy and Encyclopedia of the Telegraph, by William Maver, Jr., by permission of Maver Publishing Company, New York.]

Edison made another notable contribution to multiplex telegraphy some years later in the Phonoplex. The name suggests the use of the telephone, and such indeed is the case. The necessity for this invention arose out of the problem of increasing the capacity of telegraph lines employed in "through" and "way" service, such as upon railroads. In a railroad system there are usually two terminal stations and a number of way stations. There is naturally much intercommunication, which would be greatly curtailed by a system having the capacity of only a single message at a time. The duplexes above described could not be used on a railroad telegraph system, because of the necessity of electrically balancing the line, which, while entirely feasible on a through line, would not be practicable between a number of intercommunicating points. Edison's phonoplex normally doubled the capacity of telegraph lines, whether employed on way business or through traffic, but in actual practice made it possible to obtain more than double service. It has been in practical use for many years on some of the leading railroads of the United States.

The system is a combination of telegraphic apparatus and telephone receiver, although in this case the latter instrument is not used in the generally understood manner. It is well known that the diaphragm of a telephone vibrates with the fluctuations of the current energizing the magnet beneath it. If the make and break of the magnetizing current be rapid, the vibrations being within the limits of the human ear, the diaphragm will produce an audible sound; but if the make and break be as slow as with ordinary Morse transmission, the diaphragm will be merely flexed and return to its original form without producing a sound. If, therefore, there be placed in the same circuit a regular telegraph relay and a special telephone, an operator may, by manipulating a key, operate the relay (and its sounder) without producing a sound in the telephone, as the makes and breaks of the key are far below the limit of audibility. But if through the same circuit, by means of another key suitably connected there is sent the rapid changes in current from an induction-coil, it will cause a series of loud clicks in the telephone, corresponding to the signals transmitted; but this current is too weak to affect the telegraph relay. It will be seen, therefore, that this method of duplexing is practiced, not by varying the strength or polarity, but by sending TWO KINDS OF CURRENT over the wire. Thus, two sets of Morse signals can be transmitted by two operators over one line at the same time without interfering with each other, and not only between terminal offices, but also between a terminal office and any intermediate office, or between two intermediate offices alone.



III

AUTOMATIC TELEGRAPHY

FROM the year 1848, when a Scotchman, Alexander Bain, first devised a scheme for rapid telegraphy by automatic methods, down to the beginning of the seventies, many other inventors had also applied themselves to the solution of this difficult problem, with only indifferent success. "Cheap telegraphy" being the slogan of the time, Edison became arduously interested in the subject, and at the end of three years of hard work produced an entirely successful system, a public test of which was made on December 11, 1873 when about twelve thousand (12,000) words were transmitted over a single wire from Washington to New York. in twenty-two and one-half minutes. Edison's system was commercially exploited for several years by the Automatic Telegraph Company, as related in the preceding narrative.

As a premise to an explanation of the principles involved it should be noted that the transmission of telegraph messages by hand at a rate of fifty words per minute is considered a good average speed; hence, the availability of a telegraph line, as thus operated, is limited to this capacity except as it may be multiplied by two with the use of the duplex, or by four, with the quadruplex. Increased rapidity of transmission may, however, be accomplished by automatic methods, by means of which, through the employment of suitable devices, messages may be stamped in or upon a paper tape, transmitted through automatically acting instruments, and be received at distant points in visible characters, upon a similar tape, at a rate twenty or more times greater—a speed far beyond the possibilities of the human hand to transmit or the ear to receive.

In Edison's system of automatic telegraphy a paper tape was perforated with a series of round holes, so arranged and spaced as to represent Morse characters, forming the words of the message to be transmitted. This was done in a special machine of Edison's invention, called a perforator, consisting of a series of punches operated by a bank of keys—typewriter fashion. The paper tape passed over a cylinder, and was kept in regular motion so as to receive the perforations in proper sequence.

The perforated tape was then placed in the transmitting instrument, the essential parts of which were a metallic drum and a projecting arm carrying two small wheels, which, by means of a spring, were maintained in constant pressure on the drum. The wheels and drum were electrically connected in the line over which the message was to be sent. current being supplied by batteries in the ordinary manner.

When the transmitting instrument was in operation, the perforated tape was passed over the drum in continuous, progressive motion. Thus, the paper passed between the drum and the two small wheels, and, as dry paper is a non-conductor, current was prevented from passing until a perforation was reached. As the paper passed along, the wheels dropped into the perforations, making momentary contacts with the drum beneath and causing momentary impulses of current to be transmitted over the line in the same way that they would be produced by the manipulation of the telegraph key, but with much greater rapidity. The perforations being so arranged as to regulate the length of the contact, the result would be the transmission of long and short impulses corresponding with the dots and dashes of the Morse alphabet.

The receiving instrument at the other end of the line was constructed upon much the same general lines as the transmitter, consisting of a metallic drum and reels for the paper tape. Instead of the two small contact wheels, however, a projecting arm carried an iron pin or stylus, so arranged that its point would normally impinge upon the periphery of the drum. The iron pin and the drum were respectively connected so as to be in circuit with the transmission line and batteries. As the principle involved in the receiving operation was electrochemical decomposition, the paper tape upon which the incoming message was to be received was moistened with a chemical solution readily decomposable by the electric current. This paper, while still in a damp condition, was passed between the drum and stylus in continuous, progressive motion. When an electrical impulse came over the line from the transmitting end, current passed through the moistened paper from the iron pin, causing chemical decomposition, by reason of which the iron would be attacked and would mark a line on the paper. Such a line would be long or short, according to the duration of the electric impulse. Inasmuch as a succession of such impulses coming over the line owed their origin to the perforations in the transmitting tape, it followed that the resulting marks upon the receiving tape would correspond thereto in their respective lengths. Hence, the transmitted message was received on the tape in visible dots and dashes representing characters of the Morse alphabet.

The system will, perhaps, be better understood by reference to the following diagrammatic sketch of its general principles:

Some idea of the rapidity of automatic telegraphy may be obtained when we consider the fact that with the use of Edison's system in the early seventies it was common practice to transmit and receive from three to four thousand words a minute over a single line between New York and Philadelphia. This system was exploited through the use of a moderately paid clerical force.

In practice, there was employed such a number of perforating machines as the exigencies of business demanded. Each machine was operated by a clerk, who translated the message into telegraphic characters and prepared the transmitting tape by punching the necessary perforations therein. An expert clerk could perforate such a tape at the rate of fifty to sixty words per minute. At the receiving end the tape was taken by other clerks who translated the Morse characters into ordinary words, which were written on message blanks for delivery to persons for whom the messages were intended.

This latter operation—"copying." as it was called—was not consistent with truly economical business practice. Edison therefore undertook the task of devising an improved system whereby the message when received would not require translation and rewriting, but would automatically appear on the tape in plain letters and words, ready for instant delivery.

The result was his automatic Roman letter system, the basis for which included the above-named general principles of perforated transmission tape and electrochemical decomposition. Instead of punching Morse characters in the transmission tape however, it was perforated with a series of small round holes forming Roman letters. The verticals of these letters were originally five holes high. The transmitting instrument had five small wheels or rollers, instead of two, for making contacts through the perforations and causing short electric impulses to pass over the lines. At first five lines were used to carry these impulses to the receiving instrument, where there were five iron pins impinging on the drum. By means of these pins the chemically prepared tape was marked with dots corresponding to the impulses as received, leaving upon it a legible record of the letters and words transmitted.

For purposes of economy in investment and maintenance, Edison devised subsequently a plan by which the number of conducting lines was reduced to two, instead of five. The verticals of the letters were perforated only four holes high, and the four rollers were arranged in pairs, one pair being slightly in advance of the other. There were, of course, only four pins at the receiving instrument. Two were of iron and two of tellurium, it being the gist of Edison's plan to effect the marking of the chemical paper by one metal with a positive current, and by the other metal with a negative current. In the following diagram, which shows the theory of this arrangement, it will be seen that both the transmitting rollers and the receiving pins are arranged in pairs, one pair in each case being slightly in advance of the other. Of these receiving pins, one pair—1 and 3—are of iron, and the other pair—2 and 4—of tellurium. Pins 1-2 and 3-4 are electrically connected together in other pairs, and then each of these pairs is connected with one of the main lines that run respectively to the middle of two groups of batteries at the transmitting end. The terminals of these groups of batteries are connected respectively to the four rollers which impinge upon the transmitting drum, the negatives being connected to 5 and 7, and the positives to 6 and 8, as denoted by the letters N and P. The transmitting and receiving drums are respectively connected to earth.

In operation the perforated tape is placed on the transmission drum, and the chemically prepared tape on the receiving drum. As the perforated tape passes over the transmission drum the advanced rollers 6 or 8 first close the circuit through the perforations, and a positive current passes from the batteries through the drum and down to the ground; thence through the earth at the receiving end up to the other drum and back to the batteries via the tellurium pins 2 or 4 and the line wire. With this positive current the tellurium pins make marks upon the paper tape, but the iron pins make no mark. In the merest fraction of a second, as the perforated paper continues to pass over the transmission drum, the rollers 5 or 7 close the circuit through other perforations and t e current passes in the opposite direction, over the line wire, through pins 1 or 3, and returns through the earth. In this case the iron pins mark the paper tape, but the tellurium pins make no mark. It will be obvious, therefore, that as the rollers are set so as to allow of currents of opposite polarity to be alternately and rapidly sent by means of the perforations, the marks upon the tape at the receiving station will occupy their proper relative positions, and the aggregate result will be letters corresponding to those perforated in the transmission tape.

Edison subsequently made still further improvements in this direction, by which he reduced the number of conducting wires to one, but the principles involved were analogous to the one just described.

This Roman letter system was in use for several years on lines between New York, Philadelphia, and Washington, and was so efficient that a speed of three thousand words a minute was attained on the line between the two first-named cities.

Inasmuch as there were several proposed systems of rapid automatic telegraphy in existence at the time Edison entered the field, but none of them in practical commercial use, it becomes a matter of interest to inquire wherein they were deficient, and what constituted the elements of Edison's success.

The chief difficulties in the transmission of Morse characters had been two in number, the most serious of which was that on the receiving tape the characters would be prolonged and run into one another, forming a draggled line and thus rendering the message unintelligible. This arose from the fact that, on account of the rapid succession of the electric impulses, there was not sufficient time between them for the electric action to cease entirely. Consequently the line could not clear itself, and became surcharged, as it were; the effect being an attenuated prolongation of each impulse as manifested in a weaker continuation of the mark on the tape, thus making the whole message indistinct. These secondary marks were called "tailings."

For many years electricians had tried in vain to overcome this difficulty. Edison devoted a great deal of thought and energy to the question, in the course of which he experimented through one hundred and twenty consecutive nights, in the year 1873, on the line between New York and Washington. His solution of the problem was simple but effectual. It involved the principle of inductive compensation. In a shunt circuit with the receiving instrument he introduced electromagnets. The pulsations of current passed through the helices of these magnets, producing an augmented marking effect upon the receiving tape, but upon the breaking of the current, the magnet, in discharging itself of the induced magnetism, would set up momentarily a counter-current of opposite polarity. This neutralized the "tailing" effect by clearing the line between pulsations, thus allowing the telegraphic characters to be clearly and distinctly outlined upon the tape. Further elaboration of this method was made later by the addition of rheostats, condensers, and local opposition batteries on long lines.

The other difficulty above referred to was one that had also occupied considerable thought and attention of many workers in the field, and related to the perforating of the dash in the transmission tape. It involved mechanical complications that seemed to be insurmountable, and up to the time Edison invented his perforating machine no really good method was available. He abandoned the attempt to cut dashes as such, in the paper tape, but instead punched three round holes so arranged as to form a triangle. A concrete example is presented in the illustration below, which shows a piece of tape with perforations representing the word "same."

The philosophy of this will be at once perceived when it is remembered that the two little wheels running upon the drum of the transmitting instrument were situated side by side, corresponding in distance to the two rows of holes. When a triangle of three holes, intended to form the dash, reached the wheels, one of them dropped into a lower hole. Before it could get out, the other wheel dropped into the hole at the apex of the triangle, thus continuing the connection, which was still further prolonged by the first wheel dropping into the third hole. Thus, an extended contact was made, which, by transmitting a long impulse, resulted in the marking of a dash upon the receiving tape.

This method was in successful commercial use for some time in the early seventies, giving a speed of from three to four thousand words a minute over a single line, but later on was superseded by Edison's Roman letter system, above referred to.

The subject of automatic telegraphy received a vast amount of attention from inventors at the time it was in vogue. None was more earnest or indefatigable than Edison, who, during the progress of his investigations, took out thirty-eight patents on various inventions relating thereto, some of them covering chemical solutions for the receiving paper. This of itself was a subject of much importance and a vast amount of research and labor was expended upon it. In the laboratory note-books there are recorded thousands of experiments showing that Edison's investigations not only included an enormous number of chemical salts and compounds, but also an exhaustive variety of plants, flowers, roots, herbs, and barks.

It seems inexplicable at first view that a system of telegraphy sufficiently rapid and economical to be practically available for important business correspondence should have fallen into disuse. This, however, is made clear—so far as concerns Edison's invention at any rate—in Chapter VIII of the preceding narrative.



IV. WIRELESS TELEGRAPHY

ALTHOUGH Mr. Edison has taken no active part in the development of the more modern wireless telegraphy, and his name has not occurred in connection therewith, the underlying phenomena had been noted by him many years in advance of the art, as will presently be explained. The authors believe that this explanation will reveal a status of Edison in relation to the subject that has thus far been unknown to the public.

While the term "wireless telegraphy," as now applied to the modern method of electrical communication between distant points without intervening conductors, is self-explanatory, it was also applicable, strictly speaking, to the previous art of telegraphing to and from moving trains, and between points not greatly remote from each other, and not connected together with wires.

The latter system (described in Chapter XXIII and in a succeeding article of this Appendix) was based upon the phenomena of electromagnetic or electrostatic induction between conductors separated by more or less space, whereby electric impulses of relatively low potential and low frequency set up in. one conductor were transmitted inductively across the air to another conductor, and there received through the medium of appropriate instruments connected therewith.

As distinguished from this system, however, modern wireless telegraphy—so called—has its basis in the utilization of electric or ether waves in free space, such waves being set up by electric oscillations, or surgings, of comparatively high potential and high frequency, produced by the operation of suitable electrical apparatus. Broadly speaking, these oscillations arise from disruptive discharges of an induction coil, or other form of oscillator, across an air-gap, and their character is controlled by the manipulation of a special type of circuit-breaking key, by means of which long and short discharges are produced. The electric or etheric waves thereby set up are detected and received by another special form of apparatus more or less distant, without any intervening wires or conductors.

In November, 1875, Edison, while experimenting in his Newark laboratory, discovered a new manifestation of electricity through mysterious sparks which could be produced under conditions unknown up to that time. Recognizing at once the absolutely unique character of the phenomena, he continued his investigations enthusiastically over two mouths, finally arriving at a correct conclusion as to the oscillatory nature of the hitherto unknown manifestations. Strange to say, however, the true import and practical applicability of these phenomena did not occur to his mind. Indeed, it was not until more than TWELVE YEARS AFTERWARD, in 1887, upon the publication of the notable work of Prof. H. Hertz proving the existence of electric waves in free space, that Edison realized the fact that the fundamental principle of aerial telegraphy had been within his grasp in the winter of 1875; for although the work of Hertz was more profound and mathematical than that of Edison, the principle involved and the phenomena observed were practically identical—in fact, it may be remarked that some of the methods and experimental apparatus were quite similar, especially the "dark box" with micrometer adjustment, used by both in observing the spark. [25]