SCIENTIFIC AMERICAN SUPPLEMENT NO. 647



NEW YORK, MAY 26, 1888

Scientific American Supplement. Vol. XXV., No. 647.

Scientific American established 1845

Scientific American Supplement, $5 a year.

Scientific American and Supplement, $7 a year.

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TABLE OF CONTENTS.

PAGE.

I. ARCHITECTURE.—Elements of Architectural Design.—By H. H. Statham.—Continuation of this important contribution to building art, Gothic, Roman, Romanesque, and Mediaeval architecture compared.—26 illustrations. 10339

The Evolution of the Modern Mill.—By C. J. H. Woodbury.—Sibley College lecture treating of the buildings for mills. 10329

II. CHEMISTRY.—An Automatic Still.—By T. Maben.—An improved apparatus for making distilled water.—1 illustration. 10335

Testing Indigo Dyes.—Simple and practical chemical tests of indigo products. 10342

III. CIVIL ENGINEERING.—Railway Bridge at Lachine.—Great steel bridge across the St. Lawrence near Montreal.—2 illustrations. 10333

IV. ELECTRICITY.—Influence Machines.—By Mr. James Wimshurst.—A London Royal Institution lecture, of great value as giving a full account of the recent forms of generators of static electricity.—14 illustrations. 10327

V. HYGIENE.—The Care of the Eyes.—By Prof. David Webster, M.D.—A short and thoroughly practical paper on the all important subject of preservation of sight. 10341

VI. MECHANICAL ENGINEERING.—Economy Trials of a Non-condensing Steam Engine.—By Mr. P. W. Winans, M.I.C.E.—Interesting notes on testing steam engines. 10331

The Mechanical Equivalent of Heat.—By Prof. De Volson Wood.—A review of Mr. Hanssen's recent paper, with interesting discussion of the problem. 10331

VII. METEOROLOGY.—The Meteorological Station on Mt. Santis.—A new observatory recently erected in Switzerland, at an elevation of 8,202 feet above the sea.—1 illustration. 10341

VIII. NAVAL ENGINEERING.—Improved Screw Propeller.—Mr. B. Dickinson's new propeller.—Its form and peculiarities and results.—4 illustrations. 10333

IX. PHOTOGRAPHY.—Manufacture of Photographic Sensitive Plates.—Description of a factory recently erected for manufacturing dry plates.—The arrangement of rooms, machinery, and process.—10 illustrations. 10336

X. TECHNOLOGY.—Cotton Seed Oil.—How cotton seed oil is made, and the cost and profits of the operation. 10335

Improved Dobby.—An improved weaving apparatus described and illustrated.—1 Illustration. 10333

Sulphur Mines in Sicily.—By Philip Carroll, U. S. Consul, Florence.—How sulphur is made in Sicily, percentage, composition of the ore, and full details. 10334

The Use of Ammonia as a Refrigerating Agent.—By Mr. T. B. Lightfoot, M.I.C.E.—An elaborate discussion of the theory and practice of ammonia refrigerating, including the hydrous and anhydrous systems, with conditions of economy. 10337

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INFLUENCE MACHINES.[1]

[Footnote 1: Lecture delivered at the Royal Institution, April 27, 1888. For the above and for our illustrations we are indebted to Engineering.]

BY MR. JAMES WIMSHURST.

I have the honor this evening of addressing a few remarks to you upon the subject of influence machines, and the manner in which I propose to treat the subject is to state as shortly as possible, first, the historical portion, and afterward to point out the prominent characteristics of the later and the more commonly known machines. The diagrams upon the screen will assist the eye to the general form of the typical machines, but I fear that want of time will prevent me from explaining each of them.

In 1762 Wilcke described a simple apparatus which produced electrical charges by influence, or induction, and following this the great Italian scientist Alexander Volta in 1775 gave the electrophorus the form which it retains to the present day. This apparatus may be viewed as containing the germ of the principle of all influence machines yet constructed.

Another step in the development was the invention of the doubler by Bennet in 1786. He constructed metal plates which were thickly varnished, and were supported by insulating handles, and which were manipulated so as to increase a small initial charge. It may be better for me to here explain the process of building up an increased charge by electrical influence, for the same principle holds in all of the many forms of influence machines.

This Volta electrophorus, and these three blackboards, will serve for the purpose. I first excite the electrophorus in the usual manner, and you see that it then influences a charge in its top plate; the charge in the resinous compound is known as negative, while the charge induced in its top plate is known as positive. I now show you by this electroscope that these charges are unlike in character. Both charges are, however, small, and Bennet used the following system to increase them.

Let these three boards represent Bennet's three plates. To plate No. 1 he imparted a positive charge, and with it he induced a negative charge in plate No. 2. Then with plate No. 2 he induced a positive charge in plate No. 3. He then placed the plates Nos. 1 and 3 together, by which combination he had two positive charges within practically the same space, and with these two charges he induced a double charge in plate No. 2. This process was continued until the desired degree of increase was obtained. I will not go through the process of actually building up a charge by such means, for it would take more time than I can spare.

In 1787 Carvallo discovered the very important fact that metal plates when insulated always acquire slight charges of electricity; following up those two important discoveries of Bennet and Carvallo, Nicholson in 1788 constructed an apparatus having two disks of metal insulated and fixed in the same plane. Then by means of a spindle and handle, a third disk, also insulated, was made to revolve near to the two fixed disks, metallic touches being fixed in suitable positions. With this apparatus be found that small residual charges might readily be increased. It is in this simple apparatus that we have the parent of influence machines (see Fig. 1), and as it is now a hundred years since Nicholson described this machine in the Phil. Trans., I think it well worth showing a large sized Nicholson machine at work to-night (see Fig. 11, above).



In 1823 Ronalds described a machine in which the moving disk was attached to and worked by the pendulum of a clock. It was a modification of Nicholson's doubler, and he used it to supply electricity for telegraph working. For some years after these machines were invented no important advance appears to have been made, and I think this may be attributed to the great discoveries in galvanic electricity which were made about the commencement of this century by Galvani and Volta, followed in 1831 to 1857 by the magnificent discoveries of Faraday in electro-magnetism, electro-chemistry, and electro-optics, and no real improvement was made in influence machines till 1860, in which year Varley patented a form of machine shown in Fig. 2. It also was designed for telegraph working.

In 1865 the subject was taken up with vigor in Germany by Toepler, Holtz, and other eminent men. The most prominent of the machines made by them are figured in the diagrams (Figs. 3 to 6), but time will not admit of my giving an explanation of the many points of interest in them; it being my wish to show you at work such of the machines as I may be able, and to make some observations upon them.

In 1866 Bertsch invented a machine, but not of the multiplying type; and in 1867 Sir William Thomson invented the form of machine shown in Fig. 7, which, for the purpose of maintaining a constant potential in a Leyden jar, is exceedingly useful.

The Carre machine was invented in 1868, and in 1880 the Voss machine was introduced, since which time the latter has found a place in many laboratories. It closely resembles the Varley machine in appearance, and the Toepler machine in construction.

In condensing this part of my subject, I have had to omit many prominent names and much interesting subject matter, but I must state that in placing what I have before you, many of my scientific friends have been ready to help and to contribute, and, as an instance of this, I may mention that Prof. Sylvanus P. Thompson at once placed all his literature and even his private notes of reference at my service.

I will now endeavor to point out the more prominent features of the influence machines which I have present, and, in doing so, I must ask a moment's leave from the subject of my lecture to show you a small machine made by that eminent worker Faraday, which, apart from its value as his handiwork, so closely brings us face to face with the imperfect apparatus with which he and others of his day made their valuable researches.

The next machine which I take is a Holtz. It has one plate revolving, the second plate being fixed. The fixed plate, as you see, is so much cut away that it is very liable to breakage. Paper inductors are fixed upon the back of it, while opposite the inductors, and in front of the revolving plate, are combs. To work the machine (1) a specially dry atmosphere is required; (2) an initial charge is necessary; (3) when at work the amount of electricity passing through the terminals is great; (4) the direction of the current is apt to reverse; (5) when the terminals are opened beyond the sparking distance, the excitement rapidly dies away; (6) it does not part with free electricity from either of the terminals singly.

It has no metal on the revolving plates, nor any metal contacts; the electricity is collected by combs which take the place of brushes, and it is the break in the connection of this circuit which supplies a current for external use. On this point I cannot do better than quote an extract from page 339 of Sir William Thomson's "Papers on Electrostatics and Magnetism," which runs: "Holtz's now celebrated electric machine, which is closely analogous in principle to Varley's of 1860, is, I believe, a descendant of Nicholson's. Its great power depends upon the abolition by Holtz of metallic carriers and metallic make-and-break-contacts. It differs from Varley's and mine by leaving the inductors to themselves, and using the current in the connecting arc."

In respect to the second form of Holtz machine (Fig. 4) I have very little information, for since it was brought to my notice nearly six years ago I have not been able to find either one of the machines or any person who had seen one. As will be seen by the diagram, it has two disks revolving in opposite directions, it has no metal sectors and no metal contacts. The "connecting arc circuit" is used for the terminal circuit. Altogether I can very well understand and fully appreciate the statement made by Professor Holtz in Uppenborn's Journal of May, 1881, wherein he writes that "for the purpose of demonstration I would rather be without such machines."

The first type of Holtz machine has now in many instances been made up in multiple form, within suitably constructed glass cases, but when so made up, great difficulty has been found in keeping each of the many plates to a like excitement. When differently excited, the one set of plates furnished positive electricity to the comb, while the next set of plates gave negative electricity; as a consequence, no electricity passed the terminal.

To overcome this objection, to dispense with the dangerously cut plates, and also to better neutralize the revolving plate, throughout its whole diameter, I made a large machine having twelve disks 2 ft. 7 in. in diameter, and in it I inserted plain rectangular slips of glass between the disks, which might readily be removed; these slips carried the paper inductors. To keep all the paper inductors on one side of the machine to a like excitement, I connected them together by a metal wire. The machine so made worked splendidly, and your late president, Mr. Spottiswoode, sent on two occasions to take note of my successful modifications. The machine is now ten years old, but still works perfectly. I will show you a smaller sized one at work.

The next machine for observations is the Carre (Fig. 8). It consists essentially or a disk of glass which is free to revolve without touch or friction. At one end of a diameter it moves near to the excited plate of a frictional machine, while at the opposite end of the diameter is a strip of insulting material, opposite which, and also opposite the excited amalgam plate, are combs for conducting the induced charges, and to which the terminals are metallically connected; the machine works well in ordinary atmosphere, and certainly is in many ways to be preferred to the simple frictional machine. In my experiments with it I found that the quantity of electricity might be more than doubled by adding a segment of glass between the amalgam cushions and the revolving plate. The current in this type of machine is constant.

The Voss machine has one fixed plate and one revolving plate. Upon the fixed plate are two inductors, while on the revolving plate are six circular carriers. Two brushes receive the first portions of the induced charges from the carriers, which portions are conveyed to the inductors. The combs collect the remaining portion of the induced charge for use as an outer circuit, while the metal rod with its two brushes neutralizes the plate surface in a line of its diagonal diameter. When at work it supplies a considerable amount of electricity. It is self-exciting in ordinary dry atmosphere. It freely parts with its electricity from either terminal, but when so used the current frequently changes its direction, hence there is no certainty that a full charge has been obtained, nor whether the charge is of positive or negative electricity.

I next come to the type of machine with which I am more closely associated, and I may preface my remarks by adding that the invention sprang solely from my experience gained by constantly using and experimenting with the many electrical machines which I possessed. It was from these I formed a working hypothesis which led me to make my first small machine. It excited itself when new with the first revolution. It so fully satisfied me with its performance that I had four others made, the first of which I presented to this Institution. Its construction is of a simple character. The two disks of glass revolve near to each other and in opposite directions. Each disk carries metallic sectors; each disk has its two brushes supported by metal rods, the rods to the two plates forming an angle of 90 deg. with each other. The external circuit is independent of the brushes, and is formed by the combs and terminals.



The machine is self-exciting under all conditions of atmosphere, owing probably to each plate being influenced by and influencing in turn its neighbor, hence there is the minimum surface for leakage. When excited, the direction of the current never changes; this circumstance is due, probably, to the circuit of the metallic sectors and the make and break contacts always being closed, while the combs and the external circuit are supplemental, and for external use only. The quantity of electricity is very large and the potential high. When suitably arranged, the length of spark produced is equal to nearly the radius of the disk. I have made them from 2 in. to 7 ft. in diameter, with equally satisfactory results. The diagram, Fig. 9, shows the distribution of the electricity upon the plate surfaces when the machine is fully excited. The inner circle of signs corresponds with the electricity upon the front surface of the disk. The two circles of signs between the two black rings refer to the electricity between the disks, while the outer circle of signs corresponds with the electricity upon the outer surface of the back disk. The diagram is the result of experiments which I cannot very well repeat here this evening, but in support of the distribution shown on the diagram, I will show you two disks at work made of a flexible material, which when driven in one direction close together at the top and the bottom, while in the horizontal diameter they are repelled. When driven in the reverse direction, the opposite action takes place.

I have also experimented with the cylindrical form of the machine (see Fig. 10). The first of these I made in 1882, and it is before you. The cylinder gives inferior results to the simple disks, and is more complicated to adjust. You notice I neither use nor recommend vulcanite, and it is perhaps well to caution my hearers against the use of that material for the purpose, for it warps with age, and when left in the daylight it changes and becomes useless.



I have now only to speak of the larger machines. They are in all respects made up with the same plates, sectors, and brushes as were used by me in the first experimental machines, but for convenience sake they are fitted in numbers within a glass case. One machine has eight plates of 2 ft. 4 in. diameter; it has been in the possession of the Institution for about three years. A second, which has been made for this lecture, has twelve disks, each 2 ft. 6 in. in diameter. The length of spark from it is 13-5/8 in. (see Fig. 12). During the construction of the machine every care was taken to avoid electrical excitement in any of its parts, and after its completion several friends were present to witness the fitting of the brushes and the first start. When all was ready the terminals were connected to an electroscope, and the handle was moved so slowly that it occupied thirty seconds in moving one-half revolution, and at that point violent excitement appeared.

The machine has now been standing with its handle secured for about eight hours. No excitement is apparent, but still it may not be absolutely inert. Of this each one present must judge, but I will connect it with this electroscope (Figs. 13 and 14), and then move the handle slowly, so that you may see when the excitement commences and judge of its absolutely reliable behavior as an instrument for public demonstration. I may say that I have never, under any condition, found this type of machine to fail in its performance.



I now propose to show you the beautiful appearances of the discharge, and then, in order that you may judge of the relative capabilities of each of these three machines, we will work them all at the same time.

The large frictional machine which is in use for this comparison is so well known by you that a better standard could not be desired.

In conclusion, I may be permitted to say that it is fortunate I had not read the opinions of Sir William Thomson and Professor Holtz, as quoted in the earlier part of my lecture, previous to my own practical experiments. For had I read such opinions from such authorities, I should probably have accepted them without putting them to practical test. As the matter stands, I have done those things which they said I ought not to have done, and I have left undone those which they said I ought to have done, and by so doing I think you must freely admit that I have produced an electric generating machine of great power, and have placed in the hands of the physicist, for the purposes of public demonstration or original research, an instrument more reliable than anything hitherto produced.

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VIOLET COPYING INK.—Dissolve 40 parts of extract of logwood, 5 of oxalic acid and 30 parts of sulphate of aluminium, without heat, in 800 parts of distilled water and 10 parts of glycerine; let stand twenty-four hours, then add a solution of 5 parts of bichromate of potassium in 100 parts of distilled water, and again set aside for twenty-four hours. Now raise the mixture once to boiling in a bright copper boiler, mix with it, while hot, 50 parts of wood vinegar, and when cold put into bottles. After a fortnight decant it from the sediment. In thin layers this ink is reddish violet; it writes dark violet and furnishes bluish violet copies.

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SIBLEY COLLEGE LECTURES.—1887-88.

BY THE CORNELL UNIVERSITY NON-RESIDENT LECTURERS IN MECHANICAL ENGINEERING.

THE EVOLUTION OF THE MODERN MILL.[1]

[Footnote 1: The lecture was illustrated by about fifty views on the screen, which cannot be reproduced here, showing photographs of mills and mechanical drawings of the methods of construction alluded to in the lecture.]

BY C. J. H. WOODBURY, BOSTON, MASS.

The great factories of the textile industries in this country are fashioned after methods peculiarly adapted to the purposes for which they are designed, particularly as regards the most convenient placing of machinery, the distribution of power, the relation of the several processes to each other in the natural sequence of manufacture, and the arrangement of windows securing the most favorable lighting. The floors and roofs embody the most economical distribution of material, and the walls furnish examples of well known forms of masonry originating with this class of buildings.

These features of construction have not been produced by a stroke of genius on the part of any one man. There has been no Michael Angelo, no Sir Christopher Wren, whose epitaph bids the reader to look around for a monument; but the whole has been a matter of slow, steady growth, advancing by hair's breadth; and, as the result of continual efforts to adapt means to ends, an inorganic evolution has been effected, resulting in the survival of the fittest, and literally pushing the weaker to the wall.

This advance in methods has, like all inventions, resulted in the impairment of invested capital. There are hundreds of mill buildings, the wonder of their day, now used for storage because they cannot be employed to sufficient advantage in manufacturing purposes to compete with the facilities furnished by mills of later design. Thus their owners have been compelled to erect new buildings, and, as far as the original purpose of manufacturing is concerned, to abandon their old mills.

In the case of a certain cotton mill built about thirty years ago, and used for the manufacture of colored goods of fancy weave, the owners added to the plant by constructing a one story mill, which proved to be peculiarly adapted to this kind of manufacture, by reason of added stability, better light, and increased facilities for transferring the stock in process of manufacture; and they soon learned not only that the old mill could not compete with the new one, but that they could not afford to run it at any price; the annual saving in the cost of gas, as measured by the identical meter used to measure the supply to the old mill, being six per cent. on the cost of the new mill.

In another instance, one of two cordage mills burned, and a new mill of one story construction was erected in its place. The advantage of manufacture therein was so great that the owners of the property changed the remaining old mill into a storehouse; and now, as they wish to increase their business, it is to be torn down as a cumberer of the ground, to make room for a building of similar construction to the new mill.

It is true that such instances pertain more particularly to industries and lines of manufacture where competition is close and conditions are exacting. Still they apply in a greater or less degree to nearly every industrial process in which a considerable portion of the expense of manufacture consists in the application of organized labor to machines of a high degree of perfection.

These changes have been solely due to the differences in the conditions imposed by improvement in the methods of manufacture. The early mills of this country were driven by water power, and situated where that could be developed in the easiest manner. They were therefore placed in the narrow valleys of rapid watercourses. The method of applying water power in that day being strictly limited to placing the overshot or breast wheel in the race leading from the canal to the river, the mill was necessarily placed on a narrow strip of land between these two bodies of water, with the race-way running under the mill.

To meet these conditions of location, which was limited to this strip of land, the mill must be narrow and short, and the requisite floor area must be obtained by adding to the number of stories. It was essential that the roof of such a mill should be strong and well braced in order to sustain the excessive stress brought to bear upon it. The old factory roof was a curious structure, with eaves springing out of the edge of hollow cornices, the roof rising sharply until about six feet above the attic floor, with an upright course of about three feet, filled with sashes reaching to a second roof, which, at a more moderate pitch than the first slope, trended to the ridge.

The attic was reduced to an approximately square room, by placing sheathing between the columns underneath the sashes, and ceiling underneath the collar beams above; thus forming a cock-loft above and concealed spaces at the sides which diminished the practically available floor space in the attic. This cock-loft and these concealed spaces became receptacles for rubbish and harbors for vermin, both of which were frequent causes of fire.

The floors of such a mill were similar in their arrangement to those of a dwelling. Joists connecting the beams supported the floor; and the under side was covered over by sheathing or lath and plaster, thus forming, as in the case of the roof, hollow spaces which were a source of danger. This method caused at the same time an extravagant distribution of material, by the prodigal use of lumber and the unnecessary thickness of such floors, and entailed an excessive amount of masonry in the walls.

Mills built after this manner were frequently in odd dimensions; and the machinery was necessarily placed in diversified arrangement, calling forth a similar degree of wasted skill as that used in making a Chinese puzzle conform to its given boundaries. Their area depended upon the topography of the site, and their height upon the owner's pocket book. There was in Massachusetts a mill with ten floors, built on land worth at that time ten cents or less per square foot, which has been torn down and a new mill rebuilt in its place, because, since the advent of modern mills, it has failed every owner by reason of the excessive expenditure necessary for the distribution of power, for supervision, and for the transfer of stock in process, in comparison with the mills of their competitors, built with greater ground area and less number of stories.

With the advent of the steam engine as prime mover in mills, and the introduction of the turbine wheel with its trunk, affording greater facilities in the application of water power, the character of these buildings changed very materially, though still retaining many of their old features. One of the first of these changes may be noticed in the consideration which millwrights gave to the problem of fixing upon the dimensions of a mill so as to arrange the machinery in the most convenient manner. Although the floors were still hollow, there was a better distribution of material, the joists being deeper, of longer span, and resting upon the beams, thus avoiding the pernicious method of wasting lumber, and guarding against fracture by tenoning joists into the upper side of beams.

But this secondary type of mills was not honest in the matter of design. The influence of architects who attempted effects not accordant with or subservient to the practical use of the property is apparent in such mills. The most frequent of these wooden efforts at classic architecture was the common practice of representing a diminutive Grecian temple surrounding a factory bell perched in mid air. There were also windows with Romanesque arches copied from churches, and Mansard roofs, exiled from their true function of decorating the home, covering a factory without an answering line anywhere on its flat walls.

I do not mean to criticise any of these elements of design in their proper place and environment; but utility is the fundamental element in design, and should be especially noticeable in a building constructed for industrial purposes, and used solely as a source of commercial profit in such applications. Its lines therefore fulfill their true function in design in such measure as they suggest stability and convenience; and this can be obtained in such structures without the adoption of bad proportions offensive to the taste. In fact, certain decorative effects have been made with good results; but these have been wholly subordinate to the fundamental idea of utility.

The endurance with which brick will withstand frost and fires, and the disintegrating forces of nature, in addition to its resistance to crushing and the facility of construction, constitute very important reasons for its value for building purposes. But the use of this has been too often limited to plain brick in plain walls, whose monotony portrayed no artistic effect beyond that furnished by a few geometrical designs of the most primitive form of ornament, and falling far short of what the practice of recent years has shown to be possible with this material.

Additions of cast iron serve as ornaments only in the phraseology of trade catalogues; and the mixture of stone with brick shows results in flaring contrasts, producing harsh dissonance in the effect. The facades of such buildings show that this is brick, this is stone, or this is cast iron; but they always fail to impress the beholder with the idea of harmonious design. The use of finer varieties of clay in terra cotta figures laid among the brickwork furnishes a field of architectural design hardly appreciated. The heavy mass of brick, divided by regular lines of demarkation, serves as the groundwork of such ornamentation, while the suitable introduction in the proper places of the same material in terra cotta imparts the most appropriate elements of beauty in design; for clay in both forms shows alike its capacity for utility and decoration. The absorption of light by both forms of this material abates reflection, and renders its proportions more clearly visible than any other substance used in building construction.

The modern mill has been evolved out of the various exacting conditions developed in the effort to reduce the cost of production to the lowest terms. These conditions comprise in a great measure questions of stability, repairs, insurance, distribution of power, and arrangement of machinery.

In presenting to your attention some of the salient features of modern mill construction, I do not assume to offer a general treatise upon the subject; but propose to confine myself to a consideration of some topics which may not have been brought to your notice, as they are still largely matters of personal experience which have not yet found their way into the books on the subject. Much of this, especially the drawings thrown on the screen, is obtained from the experience of the manufacturers' mutual insurance companies, with which I am connected. By way of explanation, I will say that these companies confine their work to writing upon industrial property; and there is not a mechanical process, or method of building, or use of raw material, which does not have its relation to the question of hazard by fire, by reason of the elements of relative danger which it embodies.

It is indeed fortunate that it has been found by experience that those methods of building which are most desirable for the underwriter are also equally advantageous for the manufacturer. There is no pretense made at demands to compass the erection of fireproof buildings. In fact, as I have once remarked, a fireproof mill is commercially impossible, whatever effort may be made to overcome the constructive difficulties in the way of erecting and operating a mill which shall be all that the name implies. The present practice is to build a mill of slow burning construction.

FOUNDATIONS.

In considering the elements of such buildings, I wish to devote a few words to the question of foundations, because in the excessive loads imposed by this class of buildings, and in the frequent necessity of constructing them upon sites where alluvial drift or quicksands form compressible foundations, there is afforded an opportunity for the widest range of engineering skill in dealing with the problem. In such instances, a settling of the building must be foreseen and provided for, in order that it may be uniform under the whole structure. This is generally accomplished by means of independent foundations under the various points of pressure, arranged so as to give a uniform intensity of pressure upon all parts of the foundation. It is considered important to limit the load upon such foundations to two tons a square foot, although loads frequently exceed this amount.

There is a large building in New York City which has recently been reconstructed, and the foundations rearranged, where the load reached to the enormous amount of six to ten tons per square foot. It was a frequent occurrence in the class of high mills spoken of to impose loads of so much greater intensity upon the wall foundation than upon the piers under the columns of the mill, that the floors became much lower at the walls than at the middle.

The stone for such foundations should be laid in cement rather than in mortar, not merely because cement offers so much greater resistance to crushing, but because its setting is due to chemical changes occurring simultaneously throughout the mass. The hardening of mortar, on the other hand, is due to the drying out of the water mechanically contained with it, and its final setting is caused by the action of the carbonic acid gas in the air.

Although quicksands are never to be desired, yet they will sustain heavy loads if suitably confined. When inclined rock strata are met with, all horizontal components of stress should be removed by cutting steps so that the foundation stones shall lie upon horizontal beds.

Foundations are frequently impaired by the slow, insidious action of springs or of water percolating from the canal which supplies the water power for the mill; and the proper diversion of such streams should be carefully provided for.

In the question of foundations, there is much of a general nature which is applicable to all structures; but, at the same time, each case requires independent consideration of the circumstances involved.

WALLS.

In addition to what has been said, there is but little for me to offer on the subject of walls beyond the general question of stability. In mill construction, walls of uniform thickness have been displaced by pilastered walls, about sixteen inches thick at the upper story, and increasing four inches in thickness with each story below.

The remainder of the walls is from four to six inches less in thickness than at the pilasters. Frequently the outside dimensions of these pilasters are somewhat increased, giving greater stability and artistic effect. By leaving hollow flues within them, and using these flues as conductors for heated air which may be forced in by a blower, such pilasters afford a means for the most efficient method of warming the building.

Consideration must be given to the contraction of brick masonry, especially when an extension or addition is to be made to an older building. This shrinkage amounts to about three-sixteenths of an inch to the rod, an item which is of considerable importance in the floors of high buildings, where the aggregate difference is very appreciable. Some degree of annoyance is caused by neglect to consider this element of shrinkage in reference to the window and door frames, which should have a slight space above them allowing for such contraction. This contraction is often the source of serious trouble in brick buildings with stone faces, the shrinkage of the brick imposing excessive stress on the stone. Instances of this are quite frequent, especially in large public buildings, notably the capitol at Hartford and the public building at Philadelphia, where the shivering of the joints of the stone work gave undue alarm, on the general assumption that it indicated a dangerous structural weakness. The difficulty has, I believe, been entirely remedied in both cases.

The limit of good practice on loads upon brickwork is eight to ten tons per square foot, although it is true that these loads are largely exceeded at times. It is not to be shown, however, that the limits of safety in regard to desirable construction should be confined to the use of masonry for any low buildings. Structures which may be said to be equal to those of brickwork, as far as commercial risk is concerned, can be built wholly or in part of wood so as to conform to all practical conditions of safety. This statement does not apply except to low buildings of one or possibly two stories in height, where the timber cannot be subjected to the intense blast of flame occurring when a high building is on fire.

Mr. George H. Corliss, the eminent engine builder, of Providence, first built a one-story machine shop, with brick walls extending only to the base of the windows, above this the windows being very close together, with solid timber construction between them.

Another method is to place upright posts reaching from the sill to the roof timbers, and to lay three-inch plank on the outside of such posts up to the line of the windows. A sheathing on the outside plank between the timbers is laid vertically and fastened to horizontal furring strips. In some instances a small amount of mortar is placed over each of the furring strips. The reason for this arrangement is to prevent the formation of vertical flues, which are such a potent factor in the extension of fires.

WINDOWS.

Light is often limited or misapplied on account of faulty position or size of windows. The use of pilastered walls permits the introduction of larger windows, which are in most instances virtually double windows, the two pairs of sashes being set in one frame separated by a mullion. A more recent arrangement, widely adopted in English practice, is to place a swinging sash at the top of the window, which can be opened, when necessary, to assist in the ventilation, while the main sashes of the window are permanently fixed.

Rough plate glass is used in such windows, because it gives a softer and more diffused light, which is preferred to that from ordinary clear glass. White glass may be rendered translucent by a coat of white zinc and turpentine.

The top of a window should be as near the ceiling as practicable, because light entering the upper portion of a room illuminates it more evenly, and with less sharply marked shadows, than where the windows are lower down.

The walls below the windows should be sloped, in order that there may be no opportunity to use them as a resting place for material which should be placed elsewhere.

FIRE WALLS.

Brick division walls should be built so as to constitute a fire wall wherever it is practicable to do so. Such walls should project at least three feet above the roof, and should be capped by stone, terra cotta, or sheet metal. They must form a complete cut-off of all combustible material, especially at the cornices.

FIRE DOORS.

All openings in such walls must be provided with such fireproof doors as will prove reliable in time of need. Experience with iron doors of various forms of construction show that they have been utterly unreliable in resisting the heat of even a small fire. They will warp and buckle so as to open the passageway and allow the fire to pass through the doorway into the next room.

A door made of wood, completely enveloped by sheets of tinned iron, and strongly fastened to the wall, has proved to resist fire better than any door which can be applied to general use. I have seen such doors in division walls where they had successfully resisted the flame which destroyed four stories of a building filled with combustible material, without imposing any injury upon the door except the removal of the tin on the sheet iron; and the doors were kept in further service without any repairs other than a coat of paint.

The reason for this resistance to fire is that the wood, being a poor conductor of heat, will not warp and buckle under heat, and cannot burn for lack of air to support combustion. A removal of the sheet metal on such a door after a fire in a mill shows that the surface of the wood is carbonized, not burned, reduced to charcoal, but not to ashes.

Many fire doors are constructed and hung in such a manner that it is doubtful whether they could withstand a fire serious enough to require their services.

The door should be made of two thicknesses of matched pine boards of well dried stock, and thoroughly fastened with clinched nails. It should be covered with heavy tin, secured by hanging strips, and the sheets lock-jointed to each other, with the edge sheets wrapping around, so that no seam will be left on the edge.

Sliding doors are preferable to swinging doors for many reasons, especially because they cannot be interfered with by objects on the floor. But, if swinging doors are used, care should be taken that the hinges and latches are very strong, and securely fastened directly to the walls, and not to furring or anything in turn attached to the walls. The portion of the fixtures attached to the doors must be fastened by carriage bolts, and not by wood screws.

Sliding on trucks is the preferable method of hanging sliding doors, inclined two and one half inches to the foot, and bolted to the wall. The trucks should be heavy "barn door hangers," bolted to the door; and a grooved door jamb, of wood, covered with tin similar to the door, should receive it when shut. A step of wood will hold the door against the wall when closed. A threshold in the doorway retards fire from passing under the door, and also prevents the flow of water from one room to another.

These doors are usually placed in pairs, and sometimes an automatic sprinkler is placed between them.

Fire doors should always be closed at night. In some well ordered establishments there is a printed notice over each door directing the night watchmen to close such doors after them. In a storage warehouse in Boston, the fire doors are connected with the watchman's electric clock system, so that all openings of fire doors are matters of record on the dial sheet.

Fire doors should certainly be closed at times of fire; yet, that such doors are open at night fires, or left open by fleeing help at day fires, is an old story with underwriters. A simple automatic device can be used to shut such doors. It consists of two round pieces of wood with a scarfed joint held by a ferrule, forming a strut which is placed on two pins, keeping the door open, as other sticks have long since served like purposes.

The peculiarity of this arrangement is that the ferrule is not homogeneous, but is made up of four segments of brass soldered together with the alloy fusible at 163 degrees Fahr., which is widely known for its use in automatic sprinklers. When the solder yields, the rod cripples, and the door rolls down the inclined rail and shuts. At any time the door can be closed by removing one end of the rod from one of the pins and allowing it to hang from the other pin.

MILL TOWERS.

Because of economic reasons for preserving the space within the walls of the mill so that it may be to the greatest extent available for the best arrangement of machinery, the stairways should be placed outside of the building. Such stairways should not be spiral stairways, but should be made in short straight runs with square landings, because in the spiral stairway the portion of the stairs near the center is of so much steeper pitch that it renders them dangerous when the help are crowding out of the mill.

The wear of stairs from the tread of many feet presents a difficult problem. A very common practice consists in covering each tread with a thin piece of cast iron marked with diagonal scores, and generally showing the name of the mill. These treads wear out in the course of time, but for this use they answer very well, although somewhat slippery.

A wood tread gives a more secure foothold upon the stairway; and in some instances stairs have been protected by covering the treads with boards of hard wood, containing grooves about three-eighths of an inch deep, and of similar width, with a space of half an inch between them. These boards are grooved on both sides and placed on the stairs. After the front edge is worn, they are turned around so as to present the other edge to the front, and, in course of time, turned from the exposed side to do service in two positions on the other side. In this manner these tread covers are exposed to wear in four different positions.

Mill towers, besides containing the stairways, also serve other purposes, as for cloak rooms for the help. They often contain a part of the fire protective apparatus, carrying standpipes with hydrants at each floor. For this use they are easily available, and furnish a line of retreat in case a fire spreads to an extent beyond the ability of the apparatus to cope with it. These towers also furnish an excellent foundation for the elevated tank necessary for the supply of water for the fire apparatus in places unprovided with an elevated reservoir.

In view of the terrible and deplorable accidents which have occurred by reason of lack of proper stairway facilities at panics caused in time of fire, I would repeat the words of the late Amos D. Lockwood, the most eminent mill engineer which this country has yet produced, when he said to the New England Cotton Manufacturers' Association, "You have no moral right to build a mill employing a large number of help, with only one tower containing the stairways for exit."

The statute laws of several of the States require fire escapes; but it is a matter of fact that they are rarely used, because people are not often cool enough to avail themselves of that opportunity of escape. I know of one instance where a number of girls jumped out of a fourth story window, because they did not think of the stairways, and did not dare to use the fire escape. In that instance, none of the group referred to tried to go down the stairs, which did furnish a perfectly safe means of exit to a number of others.

Most of the fire escapes are put up so as to conform to the letter of the law; and in such manner that no one but a sailor or an acrobat would be likely to trust himself to them. In crowded city buildings, and in other places where the ordinary means of escape are not in duplicate, it is essential that fire escapes should be provided; but it is a great deal better to make a mill building so that they shall not be necessary as a matter of fact, even if they are put up to conform to the requirements of statute law.

REAR TOWERS.

In addition to stairways, towers are placed at the rear of the mill, for the purpose of accommodating the elevators and sanitary arrangements. It is not desirable that elevators should be boxed or surrounded with anything that would result in the construction of a flue; but it is preferable that they pass directly through the floors, with the openings protected by automatic hatchways which close whenever the elevator car is absent. In the washroom, etc., in these towers, it is desirable to protect the wood floors by means of a thin layer of asphalt.

BASEMENT FLOORS.

There are difficulties connected with the floors on or near the ground, by reason of the dry rot incident to such places. Dry rot consists in the development of fungus growth from spores existing in the wood, and waiting only the proper conditions for their germination. The best condition for this germination is the exposure to a slight degree of warmth and dampness. There have been many methods of applying antiseptic processes for the preservation of wood; but, irrespective of their varying degrees of merit, they have not come into general use on account of their cost, odor, and solubility in water.

It is necessary that wood should be freely exposed to circulation of air, in order to preserve it under the ordinary conditions met with in buildings. Whenever wood is sealed up in any way by paint or varnish, unless absolutely seasoned, and in a condition not found in heavy merchantable timber, dry rot is almost sure to ensue. Whitewash is better.

There has recently been an instance of a very large building in New York proving unsafe by reason of the dry rot generated in timbers which have been completely sealed up by application of plaster of Paris outside of the wire lath and plaster originally adopted as a protection against fire. Wire lath and plaster is one of the best methods of protecting timber against fire; and, if the outside is not sealed by a plaster of stucco or some other impermeable substance, the mortar will afford sufficient facilities for ventilation to prevent the deposition of moisture, which will in turn generate dry rot.

Where beams pass into walls, ventilation should be assured by placing a board each side of the beam while the walls are being built up, and afterward withdrawing it. In the form of hollow walls referred to, it is a common practice to run the end of the beam into the flue thus formed, in order to secure ventilation.

I am well acquainted with a large mill property, one building of which was erected a short time before the failure of the corporation, which resulted in the whole plant remaining idle several years. After the lapse of about five years this establishment was again put into operation; but before the new mill could be safely filled with machinery, it was necessary to remove all the beams which entered walls and to substitute for them new ones, because the ends were so thoroughly rotted that it would have been dangerous to impose any further loads upon the floors. When floors are within a few feet of the ground, unless the site be remarkably dry, it is essential to provide for a circulation of air, which can be done very feasibly in a textile mill by laying drain pipe through the upper part of the underpinning, forming a number of holes leading into this space, and then making a flue from this space to the picker room or any other place requiring a large amount of air. The fans of the picker room, drawing their supply from underneath the building, produce a circulation of air which keeps the timber in good condition.

It is supposed by some that there is a difference in the quality of timber according to the season in which it is felled, preference being given to winter timber, on account of the greater amount of potash and phosphoric acid which it is said to contain at that time. In some parts of Europe it is a custom to specify that the lumber should have been made from rafted timber, on account of the action of the water in killing certain species of germs. Whatever may be the merits of either of these two theories, the commercial lumber of the northern part of this country is generally felled in winter and afterward rafted.

The action of lime in the preservation of wood has always been attended with the most excellent results; although not suited to places subject to the action of water, which dissolves the lime, leaving the timber practically in its original condition. The preservative action of lime upon wood is readily shown by the admirable condition in which laths are always found. I doubt if any one ever found a decayed lath in connection with plaster.

As an example of the action of lime as a preservative of lumber. I can cite an instance of a mill in New Hampshire where the basement floor was placed in 1856, the ledge in the cellar having been blasted out for the purpose. The rock was very seamy, and abounded in water issuing from springs or percolating from the canal supplying water to the mill. The rock was blasted away to a grade two feet below the floor, and most of the space filled up again by replacing the small pieces of stone, so arranged as to form blind drains for the removal of any water which might find its way under the floor.

Toward the top of this filling, finer stones were used, then about three inches of gravel, which was covered with two inches of sand and lime. Two years ago I was at this mill when some alterations requiring the removal of the floor were in progress, and found that the lumber was still in good, sound condition, except for a superficial decay on the under side of the floor plank.

But there are frequent instances where it is necessary to place the floor directly upon the earth, without any space or loose filling underneath it, in order to save room, or to secure a firm support for machinery. By way of information upon what has actually been accomplished in this direction, I will cite instances of three floors in such positions, all of which have to my knowledge fulfilled the purpose for which they were designed.

The first instance is that of a basement floor laid twenty-one years ago, a portion of which was made by excavating one foot below the floor, six inches of coarse stone being filled in, then five inches of coal tar concrete made up with coarse gravel, and finally about one inch of fine gravel concrete. Before the concrete was laid, heavy stakes were driven through the floor about three feet apart, to which the floor timbers were nailed and leveled up. The concrete was then filled in upon the floor timbers, and thoroughly tamped and rolled out to the level of the top of the floor timbers. The under side of the floor timbers was covered with hot coal tar.

This floor is still in good condition, and has not needed repairs caused by the decay of the timber. Another portion of the floor laid at the same time and in the same manner, with the exception that cement concrete was used in the place of the coal tar, was entirely rotted out in ten years.

Another floor was made in quite a similar manner. All soil and loam was removed from the interior of the building; the whole surface was brought up to the grade with a puddle of gravel and ashes; stakes two and a half by four inches, and thirty inches in length, were driven down; and nailing strips were secured to them. Over this puddled surface a coat of concrete eight inches thick was laid, the top being flush with the upper surface of the nailing strips. This concrete was made of pebbles about two inches in diameter, well coated with coal tar, and laid in place when hot. It was then packed together by being tamped and rolled, and a thin covering of the tarred sand placed upon the top, forming a smooth, hard surface. The first floor consisted of two inches of matched spruce, grooved on both sides, and fitted with hard pine splines, five-eighths by one and one-fourth inches. On the top of this a hard pine 11/4 inch floor was laid over a course of building paper.

Another method, which is certainly more novel than either of the others, consists in supporting a floor upon a bed of resin. The underlying earth was removed, and replaced with spent moulding sand, leaving trenches for the floor timbers, which were placed upon bricks laid without mortar. Melted resin was poured into the space alongside and underneath the timbers. The floor planks were then laid upon the timbers, the tops of which were about half an inch above the level of the sand. Holes were bored into the floor plank about four feet apart, and melted resin then poured into the holes, so as to interpose a layer of resin underneath the floor plank and beams. Upon this floor a top floor of hard wood was laid in the usual manner. This floor has been used for a number of years to support a large quantity of heavy machine tools, principally planers, without yielding or depreciation due to decay, and has proved to be most satisfactory.

In some instances asphaltum or coal tar concrete floors are not covered with wood, although it is much more agreeable for the help to stand upon wooden floors. It should be remembered that all these compounds are readily softened by means of oil, and they should be protected from oil by a coat of paint when not covered with wood; the preferable method being to first apply a priming containing very little oil, or a coat of shellac, and follow with some paint mixed up with boiled linseed oil.

(To be continued.)

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THE MECHANICAL EQUIVALENT OF HEAT.

BY DE VOLSON WOOD, PROFESSOR OF ENGINEERING IN STEVENS INSTITUTE OF TECHNOLOGY.

It is clearly intimated by Mr. Hanssen, in his determination of the mechanical equivalent of heat, published in the Scientific American Supplement, No. 642, April 21, 1888, that his object is to determine the absolute value of this constant. With his data he finds it to be 771.89 foot pounds. But the determination by direct experiment gives a larger value. Thus, the most reliable experiments—those of Joule and Rowland—give values exceeding by several units that found by Hanssen. A committee of the British Association, appointed for this purpose, reported in 1876 that sixty of the most reliable of Joule's experiments gave the mean value 774.1. The experiments were made with water at a temperature of about 60 deg. F., according to the mercurial thermometer, and reduced to its value at the temperature of melting ice, according to the formula given by Regnault for the variation of the specific heat of water at varying temperature under the constant pressure of one atmosphere. According to this formula the specific heat of water increases with the temperature above the melting point of ice, so that the equivalent would be somewhat less at 32 deg. F. than at 60 deg. F. It will be found in Regnault's Relation des Experiences that he experimented on water at high temperatures, but more recently Professor Rowland has found that the specific heat of water is greater at 40 deg. F. than at 60 deg. F., thus reversing between these limits the law given by Regnault; the increase, as given by the most probable values, being, roughly, about 1/250 of its value at 60 deg. F. The proper correction due to this cause would make the equivalent over 777 foot pounds, instead of 774.1. Professor Rowland's experiments, when reduced to the same thermometer, same temperature, and same latitude as Joule's, agreed very nearly with those of the latter, being about 1/1000 part larger; so that the chief difference in the ultimate values consists in the reductions for temperature and latitude. The force of gravity being less for the lower latitudes, the number representing the mechanical equivalent will be greater for the latter, since the unit pound mass must fall through a greater number of feet to equal the same work; so that the equivalent will be greater at Paris than at Manchester. Professor Rowland also found that the degrees on the air thermometer from 40 deg. F. upward to above 60 deg. F. exceeded those on the mercurial thermometer throughout the corresponding range, and that from 40 deg. to 41 deg. the degree was between 1/150 and 1/200 of a degree larger on the air thermometer than on the mercurial. Although this fraction is too small to be observed by ordinary means, yet, if it exists, it cannot be ignored if absolute values are sought. Regnault employed the air thermometer in his experiments, while Joule used the mercurial thermometer, and if Joule's value 774.1 be increased by 1/200 of itself in order to reduce it from the equivalent of the degree on the mercurial thermometer to that on the air thermometer, we get 778 foot pounds, nearly. Rowland found from his experiments that when reduced to the air thermometer and to the latitude of Baltimore, the equivalent was nearly 783, subject to small residual errors.

Nearly all writers upon this subject—except Rankine—have considered that the mechanical equivalent of heat, in British units, was the energy necessary to raise the temperature of one pound of water from 32 deg. F. to 33 deg. F., but Rankine defines it as the heat necessary to increase the temperature of one pound of water one degree Fahrenheit from that of maximum density, or from 39 deg. F. to 40 deg. F. For ordinary practice it is immaterial which of these definitions is used, for the errors resulting therefrom are much less than those resulting from ordinary observations. But when the value is to be determined by direct experiment at the standard temperature, Rankine's limits are much to be preferred; for it is so very difficult to determine exact values by observation when the substance is near the state bordering on a change of state of aggregation, as that of changing from water to ice. Observations made at about 60 deg. F. were reduced by means of Regnault's law for the specific heat of water, as has been stated, which is expressed by the formula

4 9 c = 1 + ——— t + ——— t^{2} 10^{5} + 10^{7}

in which t denotes the temperature according to the Centigrade scale. According to this law, the mechanical equivalent would not be 0.2 of a foot pound greater at 5 deg. C. (41 deg. F.) than at 0 deg. C. (32 deg. F.); hence, if this law were correct, it would make no practical difference whether the temperature were at 0 deg. C. or 5 deg. C. This law makes the computed value at 32 deg. F. about 0.95 of a foot pound less than that determined by experiment at 60 deg. F.; whereas Rowland's experiments make it greater at 40 deg. F. by more than four foot pounds, for the air thermometer. In determining a fixed value to be used for scientific purposes, it is necessary to fix the place, the thermometer, and the particular degree on the thermometer. The place may be known by its latitude if reduced to the level of the sea. The air thermometer agrees most nearly with that of the ideally perfect gas thermometer, while the mercurial thermometer differs very much from it in some cases. Thus, Regnault found that when the air thermometer indicated 630 deg. F. above the melting point of ice (or 662 deg. F.), the mercurial thermometer indicated 651.9 deg. above the same point (683.9 deg. F.), a difference of 22 deg. F. It is apparent that the air thermometer furnishes the best standard. As for the particular degree on the scale to be used for the standard, it is apparent, from the observations above made, that the temperature corresponding to that at or near the maximum density of water is more desirable than that at the melting point of ice. The fact, also, that the specific heats at constant pressure and at constant volume are the same at the point of maximum density, as shown by theory, is an additional argument in favor of selecting this point for the standard. It thus appears that the solution of this problem, which appears simple and very definite by Mr. Hanssen's method, becomes intricate and, to a limited degree, indeterminate when subjected to the refinements of direct experiment. If the constants used by Hanssen are absolutely correct, then his result must be unquestioned; but since physical constants are subject to certain residual errors, one would as soon think of finding the specific heat of air at constant volume, by using the value of the mechanical equivalent as one of the elements, and trusting the result, as he would to trust to the computed value of the mechanical equivalent without subjecting it to the test of a direct experiment. We will, therefore, examine the constants used to see if they are the exact values of the quantities they represent.

He says they are universally accepted as correct; and this may be true, when used for general purposes, and yet not be scientifically exact. He uses 0.2377 as the specific heat of air. This is the value, to four decimals, found by Regnault. Thus, Regnault gives for the mean value of the specific heat of air

Between -30 deg. C and + 10 deg. C. 0.23771 " 0 deg. C " 100 deg. C. 0.23741 " 0 deg. C " 200 deg. C. 0.23751

And we know of no reason why one of these values should be used rather than another, except that the mean of a large range of temperatures may be more nearly correct than that of any other; and if this reason determines our choice, the number 0.2375 would be used instead of 0.2377. Although this difference is small, yet the former value would have reduced his result about 0.7 of a foot pound.

Again, he uses 0.1686 for the specific heat of air at constant volume. The value of this constant has never been found to any degree of accuracy by direct experiment, and we are still dependent upon the method established by La Place and Poisson, according to which the constant ratio of the specific heat of a gas at constant pressure to that at constant volume is found by means of the velocity of sound in the gas. The value of the ratio for air, as found in the days of La Place, was 1.41, and we have 0.2377 / 1.41 = 0.1686, the value used by Clausius, Hanssen, and many others. But this ratio is not definitely known. Rankine in his later writings used 1.408, and Tait in a recent work gives 1.404, while some experiments give less than 1.4, and others more than 1.41.

An error of one foot in a thousand in determining the velocity of sound will affect the third decimal figure one or two units. A small difference in the assumed weight of a cubic foot of air also affects the result. M. Hanssen gives 0.080743 pound as the weight at 32 deg. F. under the pressure of one atmosphere; while Rankine gives 0.080728 pound. In my own computations I use 1.406 as a more probable value of the constant sought. This will give for the specific heat of air at constant pressure

0.2375 / 1.406 = 0.1689

This is only 0.0003 of a unit greater than the value used by Hanssen, but it would have given him nearly 775, instead of 771.89.

Again, he uses 491.4 deg. F. for the absolute temperature of melting ice. The exact value of this constant is unknown; but the mean value as determined by Joule and Thomson, in their celebrated experiments with porous plugs, was 492.66 deg. F. This value would slightly change his result. It will be seen from the above that a small change in the constants used may affect by several units the computed value of the mechanical equivalent. I have computed it, using 1.406 for the ratio of the specific heat of air at constant pressure to that at constant volume, 491.13 deg. F. as the temperature of melting ice above the zero of the air thermometer, 26,214 feet for the height of a homogeneous atmosphere, and 0.2375 for the specific heat of air, and I find, by means of these constants, 778. If computed from the zero of the absolute scale, 492.66 deg. F., I find 777 to the nearest integer. Recently I have used 778. If the value given by Rowland, about 783 according to the air thermometer at 39 deg. F., should prove to be correct, it seems probable that the constant 1.406 used above would be reduced to about 1.403, or that the other constants must be changed by a small amount. The height of the homogeneous atmosphere used above, 26,214 feet, is the value used by Rankine as deduced from Regnault's figures, and only one foot less than the value used by Sir William Thomson; but the figures used by Mr. Hanssen give 26,2101/2 feet.

The method above called Hanssen's is really that of Dr. Mayer (the German professor), who in 1842 used it for determining the mechanical equivalent; but on account of erroneous data, the value found by him was much too small.

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ECONOMY TRIALS OF A NON-CONDENSING STEAM ENGINE—SIMPLE, COMPOUND, AND TRIPLE.[1]

[Footnote 1: Abstract of paper read before the Institution of Civil Engineers, March 13.]

BY MR. P. W. WILLANS, M.I.C.E.

The author described a series of economy trials, non-condensing, made with one of his central valve triple expansion engines, with one crank, having three cylinders in line. By removing one or both of the upper pistons, the engine could be easily changed into a compound or into a simple engine at pleasure. Distinct groups of trials were thus carried out under conditions very favorable to a satisfactory comparison of results.

No jackets were used, and no addition had, therefore, to be made to the figures given for feed water consumption on that account. Most of the trials were conducted by the author, but check trials were made by Mr. MacFarlane Gray, Prof. Kennedy, Mr. Druitt Halpin, Professor Unwin, and Mr. Wilson Hartnell. The work theoretically due from a given quantity of steam at given pressure, exhausting into the atmosphere, was first considered.

By a formula deduced from the [theta] [phi] diagram of Mr. MacFarlane Gray, which agreed in results with the less simple formulas of Rankine and Clausius, the pound weight of steam of various pressures required theoretically per indicated horse power were ascertained. (See annexed table.)

A description was then given of the main series of trials, all at four hundred revolutions per minute, of the appliances used, and of the means taken to insure accuracy. A few of the results were embodied in the table. The missing quantity of feed water at cut off, which, in the simple trials, rose from 11.7 per cent. at 40 lb. absolute pressure to nearly 30 per cent. at 110 lb. and at 90 lb. was 24.8 per cent., was at 90 lb. only 5 per cent. in the compound trials. In the latter, at 160 lb., it increased to 17 per cent., but, on repeating the trial with triple expansion, it fell to 5.46 per cent. or to 4.43 per cent. in another trial not included in the table.

On the other hand, from the greater loss in passages, etc., the compound engine must always give a smaller diagram, considered with reference to the steam present at cut-off, than a simple engine, and a triple a smaller diagram than a compound engine. Nevertheless, even at 80 lb. absolute pressure, the compound engine had considerable advantage, not only from lessened initial condensation, but from smaller loss from clearances, and from reducing both the amount of leakage and the loss resulting from it. These gains became more apparent with increasing wear. The greater surface in a compound engine had not the injurious effect sometimes attributed to it, and the author showed how much less the theoretical diagram was reduced by the two small areas taken out of it in a compound engine than by the single large area abstracted in a simple engine. The trials completely confirmed the view that the compound engine owed its superiority to reduced range of temperature. At the unavoidably restricted pressures of the triple trials, the losses due to the new set of passages, etc., almost neutralized the saving in initial condensation, but with increased pressure—say to 200 lb. absolute—there would evidently be considerable economy. The figures of these trials showed that the loss of pressure due to passages was far greater with high than with low pressure steam, and that pipes and passages should be proportioned with reference to the weight of steam passing, and not for a particular velocity merely.

The author described a series of calorimetric tests upon a large scale (usually with over two tons of water), the results of which were stated to be very consistent. After comparing the dates of initial condensation in cases where the density of steam, the area of exposed surface, and the range of temperature were all variables, with other cases (1) where the density was constant and (2) where the surface was constant, the author concluded that, at four hundred revolutions per minute, the amount of initial condensation depended chiefly on the range of temperature in the cylinder, and not upon the density of the steam or upon the extent of surface, and that its cause was probably the alternate heating and cooling of a small body of water retained in the cylinder. The effect of water, intentionally introduced into the air cushion cylinder, corroborated the author's views, and he showed how small a quantity of water retained in the cylinder would account for the effects observed. At lower speeds surface might have more influence. The favorable economical effect of high rotative speed, per se, was very apparent.

In a trial with a compound engine, with 130 lb. absolute pressure, the missing quantity at cut-off rose from 11.7 per cent. at 405 revolutions to 29.66 per cent. at 130 revolutions, the consumption of feed water increasing from 20.35 lb. to 23.67 lb. This saving of 14 per cent. was due solely to increase of speed. Similar trials had been made with a simple engine. In one simple trial at slow speed the missing quantity rose to 44.5 per cent. of the whole feed water.

+ -+ + -+ + -+ -+ Intended mean admission pressure Lb. 40 90 110 130 150 160 170 + -+ + -+ + + + + + + + Simple, Compound, or Triple. S. S. C. S. C. C. C. T. C. T. T. Actual mean admission pressure Lb. 40.88 92.65 87.54 106.3 109.3 130.6 149.9 151.9 158.5 158.1 172.5 Percentage ratio of actual mean pressure, referred to low pressure piston, to theoretical mean pressure 98.2 100 91.3 100.7 94.8 94.2 94.6 84.54 95.9 85.3 85.2 Indicated horse power 16.51 31.61 28.14 33.5 33 36.31 38.59 35.69 39.55 35.56 38.45 + -+ + -+ + + + + + + + Feed water actually used per indicated H.P.H. Simple Lb. 42.76 26.89 ... 26 ... ... ... ... ... ... ... Compound Lb. ... ... 34.16 ... 21.37 20.35 19.45 ... 19.19 ... ... Triple Lb. ... ... ... ... ... ... ... 19.68 ... 19.19 18.45 Steam required theoretically per 1 H.P.H. Lb. 34.67 19.24 19.86 17.9 17.65 16.25 15.23 15.16 14.87 14.9 14.36 Percentage efficiency 81.1 71.5 82.2 68.8 82.5 80 78.3 77 77.4 77.6 77.8 + -+ + -+ + + + + + + + Percentage of feed water missing at cut off in high pressure cylinder ... ... ... ... ... ... ... 5.33 ... 6.84 5.01 Ditto high pressure cylinder ... ... 5 ... 9.5 11.7 15.1 14.84 17 12.06 15.33 Ditto low pressure cylinder 11.7 24.8 15.2 29.56 16.25 19.1 20.6 22.12 21.3 22.11 24.21 Percentage of feed water missing at end of stroke in low pressure cylinder 10.4 18.83 14.25 21.53 16.59 17.55 20.69 18.01 19.55 18.81 19.25 + -+ + -+ + + + + + + +

The author compared a series of compound trials, at different powers, with 130 lb. absolute pressure, and various ratios of expansion, with a series giving approximately the same powers at a constant ratio of expansion, but with varying pressures, being practically a trial of automatic expansion against throttling. Starting with 40 indicated horse power, 130 lb. absolute pressure, four expansions, and a consumption of 20.75 lb. of water, the plan of varying the expansion, as compared with throttling, showed a gain of about 7 per cent. at 30 indicated horse power, but of a very small percentage when below half power. If the engine had an ordinary slide valve, the greater friction, added to irregular motion, would probably neutralize the saving, while if the engine were one in which initial condensation assumed more usual proportions, the gain would be probably on the side of variable pressure. Even as it was, the diagrams showed that the missing quantity became enormously large as the expansion increased. Judging only by the feed water accounted for by the indicator, the automatic engine appeared greatly the more economical, but actual measurement of the feed water disproved this. The position of the automatic engine was, however, relatively more favorable when simple than when compound.

In conclusion, the author referred to a trial with a condensing engine, at 170 lb. absolute pressure, in which the feed water used was 15.1 lb., a result evidently capable of further improvement, and to an efficiency trial of a combined central valve engine and Siemens' dynamo, made for the Admiralty, at various powers. At the highest power the ratio of external electrical horse power to indicated horse power in the engine was 82.3 per cent. Taking the thermo-dynamic efficiency of the engine at 80 per cent., that of the combined apparatus would be nearly 66 per cent.

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RAILWAY BRIDGE AT LACHINE.

The subject of our large illustration this week is a large steel bridge carrying the Central Pacific Railway over the St. Lawrence River at Lachine, near Montreal. The main features of this really magnificent structure are the two great channel spans, each 408 feet long. It will be noticed that the design combines, in a very ingenious manner, an upper and a lower deck structure, the railway track being laid on the top of the girders forming the side spans, and on the lower flanges of the channel spans, which are crossed by continuous girders, 75 feet deep, over the central pier, and supported by brackets as shown. The upper of our two engravings shows the method of constructing the principal spans, which were built outward from the side piers, while the work on the center pier was extended on each side to meet. It was built at the works of the Dominion Bridge Company, Montreal, from the design of Mr. C. Shaler Smith, the well-known American bridge engineer.—Engineering.



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IMPROVED SCREW PROPELLER.

While the last few years have seen great advances made in the designs of steamships and of their engines, little or nothing has been done in the way of improving the screw propeller. As a general rule it would appear to be taken for granted that no radical improvement could be made in the form of the propeller, although various metals have been introduced in its manufacture with the view of increasing its efficiency. For sea-going steamers, however, the shape remains the same, the variation chiefly relating to the number of blades employed. A striking departure from ordinary practice, however, has of late been made by Mr. B. Dickinson, who has invented a screw propeller which, on practical trial, has given an efficiency far in advance of the ordinary screw. This new propeller we illustrate here in Figs. C and D, while Fig. A shows an ordinary propeller. The Dickinson propeller illustrated has six blades, giving a surface of 30 square feet; it is right handed, and has pitch of 15 ft. and a diameter of 10 ft. 6 in. The ordinary screw propeller shown at Fig. A is right handed and two bladed, with a pitch at the boss of 13 ft. 6 in. and at the tip of 15 ft. It has a diameter of 10 ft. 9 in. and 32 square ft. of surface. The projected area looking forward is 22 square ft. and the projected area looking athwartship 22.84 square feet. The most graphic way of illustrating the principle of Mr. Dickinson's propeller is to take a two bladed propeller of the ordinary type as shown at Fig. A in the annexed cuts, and divide into three sections as in Fig. B, then move section No. 1 to the line position on the shaft of No. 3, and No. 3 to that of No. 1, No. 2 remaining stationary. The effect of this interchange will be that (having regard to the circle of rotation) No. 3, the rearmost section, will rotate in advance of No. 2, and No. 2 in advance of No. 1 (see Fig. C). By this arrangement the water operated on escapes freely astern from every blade—that from No. 1 passing in the wake of No. 2, while that from Nos. 2 and 1 passes in the wake of No. 3. Fig. D represents the blades with a wider spread as practically used. The advantages claimed by Mr. Dickinson for his propeller, and which are sufficiently important to be given in detail, are:



1. That the blades of each section, when the vessel is in motion, necessarily cut solid, undisturbed water, each blade operating upon precisely the same quantity of water as an individual broad blade would do, though, of course, it parts with it in one-third of the time.

2. That each sectional blade exerts the equivalent efficiency of the first or entering third portion of the breadth of an ordinary propeller blade, and that consequently the combined sections have greater effective power. It is now regarded by experts as an ascertained fact that the after or trailing portion of the broad blade is relatively non-effective as compared with the forward or entering portion.

3. When three blades are fitted, the spent water from No. 2 being delivered immediately in the wake of No. 3, and that from No. 1 in the wake of No. 2, has the effect of destroying or reducing to a minimum the back draught of sections Nos. 2 and 3, No. 1 alone being subject to this drawback. This is of greater importance than might at first thought appear, as in cases where there are three or four blades revolving in one plane, the water is drawn after the retreating blade, lessening the resistance to the face of the advancing one.

4. That by the subdivision of the blades, as arranged spirally, the water passing through within the radius of the propeller has its resisting capacity more thoroughly worked out than is possible with any propeller whose blades are all on the same plane. This view is confirmed by the visibly increased rotation of the water in the wake of the vessel.

5. That by broadening the blades or increasing the number of sections, the diameter of the propeller may be proportionately diminished without the sacrifice of engine power. This is often desirable with vessels of light draught, the complete immersion of the screw being at all times necessary to avoid waste of power.

6. The propeller being made and fitted on the shaft in sections, all that is necessary in case of accident is to replace the broken section. This in many cases could be done afloat.

7. The blades being arranged to take their water at different planes, there is the greater certainty of one or other of the sections operating upon what is termed the water of friction. This is considered an advantage.

8. Where it is desirable, the blades of the different sections can be made of varying breadth or pitch.

9. The principle of division into two or more sections applies equally to two, three, or four bladed ordinary propellers.

10. The adoption of this principle does not entail any alteration or enlargement of the screw space or bay as usually provided.

11. As a consequence of the freedom and rapidity with which the water operated upon escapes from the narrow blades, the depression at the stern of the vessel caused by the action of the ordinary propeller is greatly reduced.

12. The vibration caused by this propeller is so slight as to be hardly noticeable, thereby effecting a saving in the wear and tear of the engine and machinery. This may also be a consideration in promoting the comfort of passengers.

From a practical and working point of view we take Mr. Dickinson's chief claims to be, in the first place, the yielding of a greater speed per power employed, or an economy in obtaining an equal speed; in the second, increased, rapidity in maneuvering and stopping a vessel; and in the third, a reduction of vibration. In order to put these claims to a practical and reliable comparative test, Messrs. Weatherley, Mead & Hussey, of Saint Dunstan's Hill, London, placed at the inventor's disposal two of their new steamers, the Herongate and the Belle of Dunkerque. These are in every respect sister boats, and were built in 1887 by Messrs. Short Brothers, and engined by Mr. John Dickinson, of Sunderland. The Herongate was fitted about four months ago with the largest propeller yet made on Mr. B. Dickinson's principle, the Belle of Dunkerque having an ordinary four-bladed propeller of the latest improved type. Every precaution was taken to place the two vessels on the same footing for the purpose of a comparative test, which was recently carried out. Both vessels previously to the trial were placed on the gridiron, cleaned and painted, their boilers opened out and scaled, their steam gauges independently tested, and both vessels loaded with a similar cargo of pitch, the only difference being that the Herongate carried 11 tons more dead weight and had one inch more mean draught than the Belle of Dunkerque, while the former had been running continuously for nine months against the latter's two and a half months. On the day of the trial the vessels were lying in the Lower Hope reach, and it was decided to run them over the measured mile there with equal pressure of steam. The order of running having been arranged, the Herongate got under way first, the Belle of Dunkerque following over the same course. Steaming down against tide, the Herongate is said to have come round with remarkable ease and rapidity, and in turning on either helm, whether with or against tide, to have shown a decided advantage. Equally manifest, it is stated, was the superiority shown in bringing up the vessel by reversing, when running at full speed, thus confirming the very favorable reports previously received by the owners from their captains since the Dickinson propeller was fitted to the Herongate. Those who were on board her state that the vibration was scarcely noticeable. From a statement submitted to us it is clear that the Herongate had the turn of the scale against her in dead weight and draught, vacuum, and diagrams taken, but notwithstanding (making allowance for one faulty run due to the variations in tide) she appears to have more than held her own in the matter of speed, with a saving of 41/2 and 31/4 revolutions per minute at 140 lb. and 160 lb. steam pressure respectively. This is further confirmed by the results of a run made after the experiments were concluded, the two vessels being placed in line, and fairly started for a half hour's run over the flood with 150 lb. steam pressure. At the expiration of that time the Herongate was judged to be leading by at least half a length, her revolutions being 76, as against 80 in the Belle of Dunkerque. It was agreed by all present at these trials that the propeller had realized in full the three main working advantages claimed for it. This being the first Dickinson propeller fitted to a sea-going vessel of this size, it is quite within the limits of possibility that the present results may be improved upon in further practice. In any case we can but regard this propeller as a distinct and original departure in marine propulsion, and we congratulate Mr. Dickinson on his present success and promising future. Messrs. Weatherley, Mead & Hussey also deserve credit for their discernment, and for the spirited manner in which they have taken up Mr. Dickinson's ingenious invention. We understand that they are so satisfied with the results that they intend having one of their larger ocean-going steamers fitted with the Dickinson propeller.—Iron.

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IMPROVED DOBBY.



At the Manchester Royal Jubilee Exhibition, Messrs. Butterworth & Dickinson, Burnley, showed Catlow's patent dobby, which is illustrated above, as applied to a strong calico loom. This dobby is a double lift one, thus obtaining a wide shed, and the use of two lattice barrels connected by gearing so that they both revolve in the same direction. The jack lever is attached to the vertical levers, the top and bottom catches being worked respectively by the two barrels, and connected with the ends of the levers. To each of these catches a light blade spring is attached, which insures them being sprung upon the top of the knife, and thereby obtaining a certain lift. A series of wooden jacks or levers are employed, so as to give a varying lift to the front and back healds, in this way keeping the yarn in even tension, and preventing slack sheds. The healds are drawn down by means of a series of levers adjoining one another, and worked by means of a rocking bar driven from the tappet shaft. When the shed is being formed, the jacks are pushed down until it is fully open, and the warp is thus drawn down with the same certainty as the upward movement is made.—Industries.