The questions investigated have to do with the physical properties, such as electrical conductivity, magnetic condition, light-absorption, cohesion, and chemical affinities of matter at excessively low temperatures. It is found that in all these regards most substances are profoundly modified when excessively cooled. Thus if a piece of any pure metal is placed in an electric circuit and plunged into liquid air, its resistance to the passage of the electricity steadily decreases as the metal cools, until at the temperature of the liquid it is very trifling indeed. The conclusion seems to be justified that if the metal could be still further cooled until it reached the theoretical "absolute zero," or absolutely heatless condition, the electrical resistance would also be nil. So it appears that the heat vibrations of the molecules of a pure metal interfere with the electrical current. The thought suggests itself that this may be because the ether waves set up by the vibrating molecules conflict with the ether strain which is regarded by some theorists as constituting the electrical "current." But this simple explanation falters before further experiments which show, paradoxically enough, that the electrical resistance of carbon exactly reverses what has just been said of pure metals, becoming greater and greater as the carbon is cooled. If an hypothesis were invented to cover this case there would still remain a puzzle in the fact that alloys of metals do not act at all like the pure metals themselves, the electrical resistance of such alloys being, for the most part, unaffected by changed temperature. On the whole, then, the facts of electrical conduction at low temperatures are quite beyond the reach of present explanation. They must await a fuller knowledge of molecular conditions in general than is at present available—a knowledge to which the low-temperature work itself seems one of the surest channels.

Even further beyond the reach of present explanation are the facts as to magnetic conditions at low temperatures. Even as to the facts themselves different experimenters have differed somewhat, but the final conclusion of Professor Dewar is that, after a period of fluctuation, the power of a magnet repeatedly subjected to a liquid-air bath becomes permanently increased. Various substances not markedly magnetic at ordinary temperatures become so when cooled. Among these, as Professor Dewar discovered, is liquid oxygen itself. Thus if a portion of liquid air be further cooled until it assumes a semi-solid condition, the oxygen may be drawn from the mass by a magnet, leaving a pure nitrogen jelly. These facts are curious enough, and full of suggestion, but like all other questions having to do with magnetism, they hold for the present generation the double fascination of insoluble mystery. To be sure, one may readily enough suggest that if magnetism be really a whirl in the ether, this whirl is apparently interfered with by the waves of radiant heat; or, again, that magnetism is presumably due to molecular motions which are apparently interfered with by another kind of molecular motions which we call heat vibrations; but there is a vagueness about the terms of such guesses that leaves them clearly within the category of explanations that do not explain.

When it comes to the phenomena of light, we can, as is fitting, see our way a little more clearly, since, thanks to Thomas Young and his successors, we know pretty definitely what light really is. So when we learn that many substances change their color utterly at low temperatures—red things becoming yellow and yellow things white, for example—we can step easily and surely to at least a partial explanation. We know that the color of any object depends simply upon the particular ether waves of the spectrum which that particular substance absorbs; and it does not seem anomalous that molecules packed close together at—180 deg. of temperature should treat the ether waves differently than when relatively wide apart at an ordinary temperature. Yet, after all, that may not be the clew to the explanation. The packing of the molecules may have nothing to do with it. The real explanation may lie in the change of the ether waves sent out by the vibrating molecule; indeed, the fact that the waves of radiant heat and those of light differ only in amplitude lends color to this latter supposition. So the explanation of the changed color of the cooled substance is at best a dubious one.

Another interesting light phenomenon is found in the observed fact that very many substances become markedly phosphorescent at low temperatures. Thus, according to Professor Dewar, "gelatine, celluloid, paraffine, ivory, horn, and india-rubber become distinctly luminous, with a bluish or greenish phosphorescence, after cooling to—180 deg. and being stimulated by the electric light." The same thing is true, in varying degrees, of alcohol, nitric acid, glycerine, and of paper, leather, linen, tortoise-shell, and sponge. Pure water is but slightly luminous, whereas impure water glows brightly. On the other hand, alcohol loses its phosphorescence when a trace of iodine is added to it. In general, colored things are but little phosphorescent. Thus the white of egg is very brilliant but the yolk much less so. Milk is much brighter than water, and such objects as a white flower, a feather, and egg-shell glow brilliantly. The most remarkable substances of all, says Professor Dewar, whom I am all along quoting, are "the platinocyanides among inorganic compounds and the ketonic compounds among organic. Ammonium platinocyanide, cooled while stimulated by arc light, glows fully at—180 deg.; but on warming it glows like a lamp. It seems clear," Professor Dewar adds, "that the substance at this low temperature must have acquired increased power of absorption, and it may be that at the same time the factor of molecular friction or damping may have diminished." The cautious terms in which this partial explanation is couched suggest how far we still are from a full understanding of the interesting phenomena of phosphorescence. That a molecule should be able to vibrate in such a way as to produce the short waves of light, dissevered from the usual linking with the vibrations represented by high temperature, is one of the standing puzzles of physics. And the demonstrated increase of this capacity at very low temperatures only adds to the mystery.

There are at least two of the low-temperature phenomena, however, that seem a little less puzzling—the facts, namely, that cohesion and rigidity of structure are increased when a substance is cooled and that chemical activity is very greatly reduced, in fact almost abolished. This is quite what one would expect a priori—though no wise man would dwell on his expectation in advance of the experiments—since the whole question of liquids and solids versus gases appears to be simply a contest between cohesive forces that are tending to draw the molecules together and the heat vibration which is tending to throw them apart. As a substance changes from gas to liquid, and from liquid to solid, contracting meantime, simply through the lessening of the heat vibrations of its molecules, we might naturally expect that the solid would become more and more tenacious in structure as its molecules came closer and closer together, and at the same time became less and less active, as happens when the solid is further cooled. And for once experiment justifies the expectation. Professor De-war found that the breaking stress of an iron wire is more than doubled when the wire is cooled to the temperature of liquid air, and all other metals are largely strengthened, though none other to quite the same degree. He found that a spiral spring of fusible metal, which at ordinary temperature was quickly drawn out into a straight wire by a weight of one ounce, would, when cooled to -182 deg, support a weight of two pounds, and would vibrate like a steel spring so long as it was cool. A bell of fusible metal has a distinct metallic ring at this low temperature; and balls of iron, tin, lead, or ivory cooled to -182 deg and dropped from a height, "in all cases have the rebound greatly increased. The flattened surface of the lead is only one-third what it would be at ordinary temperature." "These conditions are due solely to the cooling, and persist only while the low temperature lasts."

If this increased strength and hardness of a contracted metal are what one would expect on molecular principles, the decreased chemical activity at low temperatures is no less natural-seeming, when one reflects how generally chemical phenomena are facilitated by the application of heat. In point of fact, it has been found that at the temperature of liquid hydrogen practically all chemical activity is abolished, the unruly fluorine making the only exception. The explanation hinges on the fact that every atom, of any kind, has power to unite with only a limited number of other atoms. When the "affinities" of an atom are satisfied, no more atoms can enter into the union unless some atoms already there be displaced. Such displacement takes place constantly, under ordinary conditions of temperature, because the vibrating atoms tend to throw themselves apart, and other atoms may spring in to take the places just vacated—such interchange, in fact, constituting the essence of chemical activity. But when the temperature is reduced the heat-vibration becomes insufficient to throw the atoms apart, hence any unions they chance to have made are permanent, so long as the low temperature is maintained. Thus it is that substances which attack one another eagerly at ordinary temperatures will lie side by side, utterly inert, at the temperature of liquid air.

Under certain conditions, however, most interesting chemical experiments have been made in which the liquefied gases, particularly oxygen, are utilized. Thus Olzewski found that a bit of wood lighted and thrust into liquid oxygen burns as it would in gaseous oxygen, and a red-hot iron wire thrust into the liquid burns and spreads sparks of iron. But more novel still was Dewar's experiment of inserting a small jet of ignited hydrogen into the vessel of liquid oxygen; for the jet continued to burn, forming water, of course, which was carried away as snow. The idea of a gas-jet burning within a liquid, and having snow for smoke, is not the least anomalous of the many strange conceptions that the low-temperature work has made familiar.

PRACTICAL RESULTS AND ANTICIPATIONS

Such are some of the strictly scientific results of the low-temperature work. But there are other results of a more directly practical kind—neither more important nor more interesting on that account, to be sure, but more directly appealing to the generality of the non-scientific public. Of these applications, the most patent and the first to be made available was the one forecast by Davy from the very first—namely, the use of liquefied gases in the refrigeration of foods. Long before the more resistant gases had been liquefied, the more manageable ones, such as ammonia and sulphurous acid, had been utilized on a commercial scale for refrigerating purposes. To-day every brewery and every large cold-storage warehouse is supplied with such a refrigerator plant, the temperature being thus regulated as is not otherwise practicable. Many large halls are cooled in a similar manner, and thus made comfortable in the summer. Ships carrying perishables have the safety of their cargoes insured by a refrigerator plant. In all large cities there are ice manufactories using the same method, and of late even relatively small establishments, hotels, and apartment houses have their ice-machine. It seems probable that before long all such buildings and many private dwellings will be provided with a cooling apparatus as regularly as they are now equipped with a heating apparatus.

The exact details of the various refrigerator machines of course vary, but all of them utilize the principles that the laboratory workers first established. Indeed, the entire refrigerator industry, now assuming significant proportions, may be said to be a direct outgrowth of that technical work which Davy and Faraday inaugurated and prosecuted at the Royal Institution—a result which would have been most gratifying to the founder of the institution could he have forecast it. The usual means of distributing the cooling fluids in the commercial plants is by the familiar iron pipes, not dissimilar in appearance (when not in operation) to the familiar gas, water, and steam pipes. When operating, however, the pipes themselves are soon hidden from view by the thick coating of frost which forms over them. In a moist beer-cellar this coating is often several inches in thickness, giving a very characteristic and unmistakable appearance.

Another commercial use to which refrigerator machines are now put is in the manufacture of various drugs, where absolute purity is desirable. As different substances congeal at different temperatures, but the same substances at uniform pressure always at the same temperature, a means is afforded of freeing a drug from impurities by freezing, where sometimes the same result cannot be accomplished with like thoroughness by any other practicable means. Indeed, by this means impurities have been detected where not previously suspected. And Professor Ramsay has detected some new elementary substances even, as constituents of the air, which had previously not been dissociated from the nitrogen with which they are usually mixed.

Such applications of the refrigerator principles as these, however, though of vast commercial importance, are held by many enthusiasts to be but a bagatelle compared with other uses to which liquefied gases may some time be put. Their expectations are based upon the enormous potentialities that are demonstrably stored in even a tiny portion of, say, liquefied air. These are, indeed, truly appalling. Consider, for example, a portion of air at a temperature above its critical point, to which, as in Thilorier's experiments, a pressure of thirty-one tons to the square inch of the encompassing wall is being applied. Recall that action and reaction are equal, and it is apparent that the gas itself is pushing back—struggling against being compressed, if you will—with an equal power. Suppose the bulk of the gas is such that at this pressure it occupies a cubical space six inches on a side—something like the bulk of a child's toy balloon, let us say. Then the total outward pressure which that tiny bulk of gas exerts, in its desperate molecular struggle, is little less than five thousand tons. It would support an enormous building without budging a hair's-breadth. If the building weighed less than five thousand tons it would be lifted by the gas; if much less it would be thrown high into the air as the gas expanded. It gives one a new sense of the power of numbers to feel that infinitesimal atoms, merely by vibrating in unison, could accomplish such a result.

But now suppose our portion of gas, instead of being placed under our hypothetical building, is plunged into a cold medium, which will permit its heat-vibrations to exhaust themselves without being correspondingly restored. Then, presently, the temperature is lowered below the critical point, and, presto! the mad struggle ceases, the atoms lie amicably together, and the gas has become a liquid. What a transformed thing it is now. Instead of pressing out with that enormous force, it has voluntarily contracted as the five thousand tons pressure could not make it do; and it lies there now, limpid and harmless-seeming, in the receptacle, for all the world like so much water.

And, indeed, the comparison with water is more than superficial, for in a cup of water also there are wonderful potentialities, as every steam-engine attests. But an enormous difference, not in principle but in practical applications, exists in the fact that the potentialities of the water cannot be utilized until relatively high temperatures are reached. Costly fuel must be burned and the heat applied to the water before it can avail to do its work. But suppose we were to place our portion of liquid air, limpid and water-like, in the cylinder of a locomotive, where the steam of water ordinarily enters. Then, though no fuel were burned—though the entire engine stood embedded in the snow of an arctic winter—it would be but a few moments before the liquid air would absorb even from this cold medium heat enough to bring it above its critical temperature; and, its atoms now dancing apart once more and re-exerting that enormous pressure, the piston of the engine would be driven back and then the entire cylinder burst into fragments as the gas sought exit. In a word, then, a portion of liquid air has a store of potential energy which can be made kinetic merely by drawing upon the boundless and free supply of heat which is everywhere stored in the atmosphere we breathe and in every substance about us. The difficulty is, not to find fuel with which to vaporize it, as in case of water, but to keep the fuel from finding it whether or no. Were liquid air in sufficient quantities available, the fuel problem would cease to have any significance. But of course liquid air is not indefinitely available, and exactly here comes the difficulty with the calculations of many enthusiasts who hail liquefied gas as the motive power of the near future. For of course in liquefying the air power has been applied, for the moment wasted, and unless we can get out of the liquid more energy than we have applied to it, there is no economy of power in the transaction. Now the simplest study of the conditions, with the mechanical theory of matter in mind, makes it clear that this is precisely what one can never hope to accomplish. Action and reaction are equal and in opposite directions at all stages of the manipulation, and hence, under the most ideal conditions, we must expect to waste as much work in condensing a gas (in actual practice more) as the condensed substance can do in expanding to the original volume. Those enthusiasts who have thought otherwise, and who have been on the point of perfecting an apparatus which will readily and cheaply produce liquid air after the first portion is produced, are really but following the old perpetual-motion-machine will-o'-the-wisp.

It does not at all follow from this, however, that the energies of liquefied air may not be utilized with enormous advantage. It is not always the cheapest form of power-transformer that is the best for all purposes, as the use of the electrical storage battery shows. And so it is quite within the possibilities that a multitude of uses may be found for the employment of liquid air as a motive power, in which its condensed form, its transportability or other properties will give it precedence over steam or electricity. It has been suggested, for example, that liquefied gas would seem to afford the motive power par excellence for the flying-machine, once that elusive vehicle is well in harness, since one of the greatest problems here is to reduce the weight of the motor apparatus. In a less degree the same problem enters into the calculations of ships, particularly ships of war; and with them also it may come to pass that a store of liquid air (or other gas) may come to take the place of a far heavier store of coal. It is even within the possibilities that the explosive powers of the same liquid may take the place of the great magazines of powder now carried on war-ships; for, under certain conditions, the liquefied gas will expand with explosive suddenness and violence, an "explosion" being in any case only a very sudden expansion of a confined gas. The use of the compressed air in the dynamite guns, as demonstrated in the Cuban campaign, is a step in this direction. And, indeed, the use of compressed air in many commercial fields already competing with steam and electricity is a step towards the use of air still further compressed, and cooled, meantime, to a condition of liquidity. The enormous advantages of the air actually liquefied, and so for the moment quiescent, over the air merely compressed, and hence requiring a powerful retort to hold it, are patent at a glance. But, on the other hand, the difficulty of keeping it liquid is a disadvantage that is equally patent. How the balance will be struck between these contending advantages and disadvantages it remains for the practical engineering inventors of the future—the near future, probably—to demonstrate.

Meantime there is another line of application of the ideas which the low-temperature work has brought into prominence which has a peculiar interest in the present connection because of its singularly Rumfordian cast, so to speak, I mean the idea of the insulation of cooled or heated objects in the ordinary affairs of life, as, for example, in cooking. The subject was a veritable hobby with the founder of the Royal Institution all his life. He studied the heat-transmitting and heat-reflecting properties of various substances, including such directly practical applications as rough surfaces versus smooth surfaces for stoves, the best color for clothing in summer and in winter, and the like. He promulgated his ideas far and wide, and demonstrated all over Europe the extreme wastefulness of current methods of using fuel. To a certain extent his ideas were adopted everywhere, yet on the whole the public proved singularly apathetic; and, especially in America, an astounding wastefulness in the use of fuel is the general custom now as it was a century ago. A French cook will prepare an entire dinner with a splinter of wood, a handful of charcoal, and a half-shovelful of coke, while the same fuel would barely suffice to kindle the fire in an American cook-stove. Even more wonderful is the German stove, with its great bulk of brick and mortar and its glazed tile surface, in which, by keeping the heat in the room instead of sending it up the chimney, a few bits of compressed coal do the work of a hodful.

It is one merit of the low-temperature work, I repeat, to have called attention to the possibilities of heat insulation in application to "the useful purposes of life." If Professor Dewar's vacuum vessel can reduce the heat-transmitting capacity of a vessel by almost ninety-seven per cent., why should not the same principle, in modified form, be applied to various household appliances—to ice-boxes, for example, and to cooking utensils, even to ovens and cook-stoves? Even in the construction of the walls of houses the principles of heat insulation might advantageously be given far more attention than is usual at present; and no doubt will be so soon as the European sense of economy shall be brought home to the people of the land of progress and inventions. The principles to be applied are already clearly to hand, thanks largely to the technical workers with low temperatures. It remains now for the practical inventors to make the "application to the useful purposes of life." The technical scientists, ignoring the example which Rumford and a few others have set, have usually no concern with such uninteresting concerns.

For the technical scientists themselves, however, the low-temperature field is still full of inviting possibilities of a strictly technical kind. The last gas has indeed been liquefied, but that by no means implies the last stage of discovery. With the successive conquest of this gas and of that, lower and lower levels of temperature have been reached, but the final goal still lies well beyond. This is the north pole of the physicist's world, the absolute zero of temperature—the point at which the heat-vibrations of matter are supposed to be absolutely stilled. Theoretically this point lies 2720 below the Centigrade zero. With the liquefaction of hydrogen, a temperature of about -253 deg or -254 deg Centigrade has been reached. So the gap seems not so very great. But like the gap that separated Nansen from the geographical pole, it is a very hard road to travel. How to compass it will be the study of all the low-temperature explorers in the immediate future. Who will first reach it, and when, and how, are questions for the future to decide.

And when the goal is reached, what will be revealed? That is a question as full of fascination for the physicist as the north-pole mystery has ever been for the generality of mankind. In the one case as in the other, any attempt to answer it to-day must partake largely of the nature of a guess, yet certain forecasts may be made with reasonable probability. Thus it can hardly be doubted that at the absolute zero all matter will have the form which we term solid; and, moreover, a degree of solidity, of tenacity and compactness greater than ever otherwise attained. All chemical activity will presumably have ceased, and any existing compound will retain unaltered its chemical composition so long as absolute zero pertains; though in many, if not in all cases, the tangible properties of the substance—its color, for example, and perhaps its crystalline texture—will be so altered as to be no longer recognizable by ordinary standards, any more than one would ordinarily recognize a mass of snowlike crystals as air.

It has, indeed, been suggested that at absolute zero all matter may take the form of an impalpable powder, the forces of cohesion being destroyed with the vibrations of heat. But experiment seems to give no warrant to this forecast, since cohesion seems to increase exactly in proportion to the decrease of the heat-vibrations. The solidity of the meteorites which come to the earth out of the depths of space, where something approaching the zero temperature is supposed to prevail, also contradicts this assumption. Still less warrant is there for a visionary forecast at one time entertained that at absolute zero matter will utterly disappear. This idea was suggested by the observation, which first gave a clew to the existence of the absolute zero, that a gas at ordinary temperatures and at uniform pressure contracts by 1-27 2d of its own bulk with each successive degree of lowered temperature. If this law held true for all temperatures, the gas would apparently contract to nothingness when the last degree of temperature was reached, or at least to a bulk so insignificant that it would be inappreciable by standards of sense. But it was soon found by the low-temperature experimenters that the law does not hold exactly at extreme temperatures, nor does it apply at all to the rate of contraction which the substance shows after it assumes the liquid and solid conditions. So the conception of the disappearance of matter at zero falls quite to the ground.

But one cannot answer with so much confidence the suggestion that at zero matter may take on properties hitherto quite unknown, and making it, perhaps, differ as much from the conventional solid as the solid differs from the liquid, or this from the gas. The form of vibration which produces the phenomena of temperature has, clearly, a determining share in the disposal of molecular relations which records itself to our senses as a condition of gaseousness, liquidity, or solidity; hence it would be rash to predict just what inter-molecular relations may not become possible when the heat-vibration is altogether in abeyance. That certain other forms of activity may be able to assert themselves in unwonted measure seems clearly forecast in the phenomena of increased magnetism, and of phosphorescence at low temperatures above outlined. Whether still more novel phenomena may put in an appearance at the absolute zero, and if so, what may be their nature, are questions that must await the verdict of experiment. But the possibility that this may occur, together with the utter novelty of the entire subject, gives the low-temperature work precedence over almost every other subject now before the world for investigation (possible exceptions being radio-activity and bacteriology). The quest of the geographical pole is but a child's pursuit compared with the quest of the absolute zero. In vital interest the one falls as far short of the other as the cold of frozen water falls short of the cold of frozen air.

Where, when, and by whom the absolute zero will be first reached are questions that may be answered from the most unexpected quarter. But it is interesting to know that great preparations are being made today in the laboratories of the Royal Institution for a further attack upon the problem. Already the research equipment there is the best in the world in this field, and recently this has been completely overhauled and still further perfected. It would not be strange, then, in view of past triumphs, if the final goal of the low-temperature workers should be first reached in the same laboratory where the outer territories of the unknown land were first penetrated three-quarters of a century ago. There would seem to be a poetic fitness in the trend of events should it so transpire. But of course poetic fitness does not always rule in the land of science.



IV. SOME PHYSICAL LABORATORIES AND PHYSICAL PROBLEMS

SIR NORMAN LOCKYER AND SOLAR CHEMISTRY

SIR NORMAN LOCKYER is professor of astronomical physics and director of the solar observatory at the Royal College of Science in South Kensington. Here it is that his chief work has been done for some thirty years past. The foundation-stone of that work is spectroscopic study of the sun and stars. In this study Professor Lockyer was a pioneer, and he has for years been recognized as the leader. But he is no mere observer; he is a generalizer as well; and he long since evolved revolutionary ideas as to the origin of the sidereal and solar systems.

For a man whose chief occupation is the study of the sun and stars, smoky, foggy, cloudy London may seem a strange location. I asked Professor Lockyer about this, and his reply was most characteristic. "The fact is," he said, "the weather here is too fine from one point of view: my working staff is so small, and the number of working nights so large, that most of the time there is no one about to do anything during the day. Then, another thing, here at South Kensington I am in touch with my colleagues in the other departments—physics, chemistry, and so forth—and can at once draw upon their special knowledge for aid on any obscure point in their lines that may crop up. If we were out in the country this would not be so. You see, then, that it is a choice between weather and brains. I prefer the brains."

Professor Lockyer went on to state, however, that he is by no means altogether dependent upon the observations made at South Kensington. For certain purposes the Royal Observatory at Greenwich is in requisition, and there are three observatories at different places in India at which photographs of the sun-spots and solar spectra are taken regularly. From these combined sources photographs of the sun are forthcoming practically every day of the year; to be accurate, on three hundred and sixty days out of the three hundred and sixty-five. It was far otherwise when Professor Lockyer first began his studies of the sun, as observations were then made and recorded on only about one-third of the days in each year.

Exteriorly the observatory at South Kensington is not at all such a place as one might expect to find. It is, in Professor Lockyer's own words, "little more than a collection of sheds," but within these alleged sheds may be found an excellent equipment of telescopes, both refracting and reflecting, and of all other things requisite to the peculiar study which forms the subject of special research here.

I have had occasion again and again to call attention to this relatively meagre equipment of the European institutions, but in no case, perhaps, is the contrast more striking between the exterior appearance of a famous scientific institution and the work that is being accomplished within it than is shown in the case of the South Kensington observatory. It should be added that this remark does not apply to the chief building of the Royal College of Science itself.

The theories for which Professor Lockyer has so long been famous are well known to every one who takes much interest in the progress of scientific ideas. They are notably the theory that there is a direct causal association between the prevalence of sun-spots and terrestrial weather; the theory of the meteoritic origin of all members of the sidereal family; and the dissociation theory of the elements, according to which our so-called elements are really compounds, capable of being dissociated into simpler forms when subjected to extreme temperatures, such as pertain in many stars. As I have said, these theories are by no means new. Professor Lockyer has made them familiar by expounding them for a full quarter of a century or more. But if not new, these theories are much too important to have been accepted at once without a protest from the scientific world. In point of fact, each of them has been met with most ardent opposition, and it would, perhaps, not be too much to say that not one of them is, as yet, fully established. It is of the highest interest to note, however, that the multitudinous observations bearing upon each of these topics during the past decade have tended, in Professor Lockyer's opinion, strongly to corroborate each one of these opinions.

Two or three years ago Sir Norman Lockyer, in association with his son, communicated to the Royal Society a paper in which the data recently obtained as to the relation between sun-spots and the weather in India—the field of observations having been confined to that territory—are fully elaborated. A remarkable feature of the recent work in that connection has been the proof, or seeming proof, that the temperature of the sun fluctuates from year to year. At times when the sun-spots are numerous and vigorous in their action, the spectrum of the elements in these spots becomes changed. During the times of minimum sun-spot activity the spectrum shows, for example, the presence of large quantities of iron in these spots—of course in a state of vapor. But in times of activity this iron disappears, and the lines which previously vouched for it are replaced by other lines spoken of as the enhanced lines of iron—that is to say, the lines which are believed to represent the unknown substance or substances into which the iron has been decomposed; and what is true of iron is true of various other elements that are detected in the sun-spots. The explanation of this phenomena, if Professor Lockyer reads the signs aright, is that during times of minimum sun-spot activity the temperature of the sun-spots is relatively cool, and that in times of activity the temperature becomes greatly increased. One must come, therefore, to speaking of hot spots and cool spots on the sun; although the cool spots, it will be understood, would hardly be considered cool in the terrestrial sense, since their temperature is sufficient to vaporize iron.

Now the point of the recent observations is that the fluctuations in the sun's heat, due to the periodic increase and subsidence of sun-spot disturbances—such fluctuations having been long recognized as having regular cyclic intervals of about eleven years—are instrumental in effecting changes in the terrestrial weather. According to the paper just mentioned, it would appear to be demonstrated that the periods of decreased rainfall in India have a direct and relatively unvarying relationship to the prevalence of the sun-spots, and that, therefore, it has now become possible, within reasonable limits, to predict some years in advance the times of famine in India. So important a conclusion as this is certainly not to be passed over lightly, and all the world, scientific and unscientific alike, will certainly watch with acute interest for the verification of this seemingly startling practical result of so occult a science as solar spectroscopy.

The theory of the decomposition of the elements is closely bound up with the meteoritic theory. In a word, it may be said of each that Professor Lockyer is firmly convinced that all the evidence that has accumulated in recent years is so strongly in favor as to bring these theories almost to a demonstration. The essence of the meteoritic theory, it will be recalled, is that all stars have their origin in nebulae which consist essentially of clouds of relatively small meteorites. It will be recalled further that Professor Lockyer long ago pointed out that stars pass through a regular series of changes as to temperature, with corresponding changes of structure, becoming for a time hotter and hotter until a maximum is reached, and then passing through gradual stages of cooling until their light dies out altogether. Very recently Professor Lockyer has been enabled, through utilization of the multiform records accumulated during years of study, to define the various typical stages of the sidereal evolution; and not merely to define them but to illustrate them practically by citing stars which belong to each of these stages, and to give them yet clearer definition by naming the various elements which the spectroscope reveals as present in each.

His studies have shown that the elements do not always give the same spectrum under all conditions; a result quite at variance with the earlier ideas on the subject. Even in the terrestrial laboratory it is possible to subject various metals, including iron, to temperatures attained with the electric spark at which the spectrum becomes different from that, for example, which was attained with the lower temperature of the electric arc. Through these studies so-called series-spectra have been attained for various elements, and a comparison of these series-spectra with the spectra of various stars has led to the conclusion that many of the unknown lines previously traced in the spectra of such stars are due to the decomposition products of familiar elements; all of which, of course, is directly in line of proof of the dissociation hypothesis.

Another important result of Professor Lockyer's very recent studies has come about through observation of the sun in eclipse. A very interesting point at issue all along has been the question as to what layers of the sun's atmosphere are efficient in producing the so-called reverse lines of the spectrum. It is now shown that the effect is not produced, as formerly supposed, by the layers of the atmosphere lying just above the region which Professor Lockyer long ago named the chromosphere, but by the gases of higher regions. Reasoning from analogy, it may be supposed that a corresponding layer of the atmosphere of other stars is the one which gives us the reverse spectrum of those stars. The exact composition of this layer of the sidereal atmosphere must, of course, vary with the temperature of the different stars, but in no case can we expect to receive from the spectroscope a full record of all the substances that may be present in other layers of the atmosphere or in the body of the star itself. Thus, for example, the ordinary Freuenhofer spectrum of the sun shows us no trace of the element helium, though through other observations at the time of eclipse Professor Lockyer had discovered that element there, as we have seen, some thirty years before anything was known of it on the earth.

In a recent eclipse photographs were taken of the spectra of the lower part of the sun's atmosphere by itself, and it was found that the spectrum of this restricted area taken by itself gave the lines which specialize the spectra of so different a star as Procyon. "I recognize in the result," says Professor Lockyer, "a veritable Rosetta Stone which will enable us to read the celestial hieroglyphics presented to us in stellar spectra, and help us to study the spectra and to get at results much more distinctly and certainly than ever before."

But the most striking confirmation which the meteoritic hypothesis has received has come to hand through study of the spectrum of the new star which appeared in the constellation Perseus in February, 1901, and which was so widely heralded everywhere in the public press. This star was discovered on the morning of February 22d by star-gazers in Scotland, and in America almost simultaneously. It had certainly not been visible a few hours before, and it had blazed up suddenly to a greater brilliancy than that of a first-magnitude star. At first it was bluish-white in color, indicating an extremely high temperature, but it rapidly subsided in brilliancy and assumed a red color as it cooled, passing thus, in the course of a few days, through stages for which ordinary stars require periods of many millions of years.

The most interesting feature of the spectrum of this new star was the fact that it showed both light and dark lines for the same substances, the two lying somewhat apart. This means, being interpreted, that some portions of a given substance are giving out light, thus producing the bright lines of the spectrum, and that other portions of the same substance are stopping certain rays of transmitted light, thus producing the dark lines. The space between the bright and dark lines, being measured, indicated that there was a differential motion between the two portions of substance thus recorded of something like seven hundred miles a second. This means, according to theory—and it seems hardly possible to explain it otherwise—that two sidereal masses, one at least of which was moving at an enormous rate of speed, had collided, such collision, of course, being the cause of the incandescence that made the mass suddenly visible from the earth as a new star.

New stars are by no means every-day affairs, there having been but thirty-two of them recorded in the world's history, and of these only two have exceeded the present one in brilliancy. As a mere spectacle, therefore, this new star was of great interest; but a far greater importance attaches to it through the fact that it conforms so admirably to the course that meteoritic hypothesis would predict for it. "That is what confounds my opponents," said Professor Lockyer, in talking to me about the new star. "Most of those who oppose my theory have not taken the trouble to make observations for themselves, but have contented themselves with falling back apparently on the postulate that because a theory is new it must be wrong. Then, outside the scientific world, comparatively few people appreciate the extreme parsimony of nature. They expect, therefore, that when such a phenomenon as the appearance of a new star occurs, the new-comer will establish new rules for itself and bring chaos into the scientific world. But in point of fact nature never does things in two ways if she can possibly do them in one, and the most striking thing about the new stars is that all the phenomena they present conform so admirably to the laws built up through observation of the old familiar stars. As to our particular theories, we here at South Kensington"—it will be understood that this use of the editorial "we" is merely a modest subterfuge on the part of Professor Lockyer—"have no regard for them at all simply as ours. Like all scientists worthy the name, we seek only the truth, and should new facts come along that seem to antagonize our theory we should welcome them as eagerly as we welcome all new facts of whatever bearing. But the truth is that no such new facts have appeared in all these years, but that, on the contrary, the meteoritic hypothesis has received ever-increasing support from most unexpected sources, from none more brilliantly or more convincingly than from this new star in Perseus." And I suspect that as much as this at least—if not indeed a good deal more—will be freely admitted by every candid investigator of Sir Norman Lockyer's theory.

SIR WILLIAM RAMSAY AND THE NEW GASES

The seat of Sir William Ramsay's labors is the University College, London. The college building itself, which is located on Gower Street, is, like the British Museum, reminiscent or rather frankly duplicatory in its columned architecture of the classical. Interiorly it is like so many other European institutions in its relative simplicity of equipment. One finds, for example, Professor Ramsay and Dr. Travers generating the hydrogen for their wonderful experiments in an old beer-cask. Professor Ramsay himself is a tall, rather spare man, just entering the gray stage of life, with the earnest visage of the scholar, the keen, piercing eye of the investigator—yet not without a twinkle that justifies the lineage of the "canny Scot." He is approachable, affable, genial, full of enthusiasm for his work, yet not taking it with such undue seriousness as to rob him of human interest—in a word, the type of a man of science as one would picture him in imagination, and would hope, with confident expectation, to find him in reality.

I have said that the equipment of the college is somewhat primitive, but this must not be taken too comprehensively. Such instances as that of the beer-cask show, to be sure, an adaptation of means to ends on economical lines; yet, on the other hand, it should not be forgotten that the beer-cask serves its purpose admirably; and, in a word, it may be said that Professor Ramsay's laboratory contains everything that is needed to equip it fully for the special work to which it has been dedicated for some years past. In general, it looks like any other laboratory—glass tubes, Bunsen burners, retorts and jars being in more or less meaningless tangles; but there are two or three bits of apparatus pretty sure to attract the eye of the casual visitor which deserve special mention. One of these is a long, wooden, troughlike box which extends across the room near the ceiling and is accessible by means of steps and a platform at one end. Through this boxlike tube the chief expert in spectroscopy (Dr. Bay-ley) spies on the spectrum of the gas, and learns some of its innermost secrets. But an even more mystifying apparatus is an elaborate array of long glass tubes, some of them carried to the height of several feet, interspersed with cups of mercury and with thermometers of various sizes and shapes. The technical scientist would not make much of this description, but neither would an untechnical observer make much of the apparatus; yet to Dr. Travers, its inventor, it is capable of revealing such extraordinary things as the temperature of liquid hydrogen—a temperature far below that at which the contents of even an alcoholic thermometer are solidified; at which, indeed, the prime constituents of the air suffer a like fate. The responsible substance which plays the part of the familiar mercury, or alcohol, in Dr. Travers's marvellous thermometer is hydrogen gas. The principle by which it is utilized does not differ, in its rough essentials, from that of ordinary thermometers, but the details of its construction are much too intricate to be elaborated here.

But if you would see the most wonderful things in this laboratory—or rather, to be quite accurate, I should say, if you would stand in the presence of the most wonderful things—you must go with Professor Ramsay to his own private laboratory, and be introduced to some little test-tubes that stand inverted in cups of mercury decorating a shelf at one end. You would never notice these tubes of your own accord were you to browse ever so long about the room. Even when your attention is called to them you still see nothing remarkable. These are ordinary test-tubes inverted over ordinary mercury. They contain something, since the mercury does not rise in them completely, but if that something be other than ordinary air there is nothing about its appearance, or rather lack of appearance, to demonstrate it. But your interest will hardly fail to be arrested when Professor Ramsay, indicating one and another of these little tubes, says: "Here you see, or fail to see, all the krypton that has ever been in isolated existence in the world, and here all the neon, and here, again, all the zenon."

You will understand, of course, that krypton, neon, and zenon are the new gases of the atmosphere whose existence no one suspected until Professor Ramsay ferreted them out a few years ago and isolated them. In one sense there should be nothing mysterious about substances that every air-breathing creature on the globe has been imbibing pretty constantly ever since lungs came into fashion. But in another view the universal presence of these gases in the air makes it seem all the more wonderful that they could so long have evaded detection, considering that chemistry has been a precise science for more than a century. During that time thousands of chemists have made millions of experiments in the very midst of these atmospheric gases, yet not one of the experimenters, until recently, suspected their existence. This proves that these gases are no ordinary substances—common though they be. Personally I have examined many scientific exhibits in many lands, but nowhere have I seen anything that filled my imagination with so many scientific visions as these little harmless test-tubes at the back of Professor Ramsay's desk. Perhaps I shall attempt to visualize some of these imaginings before finishing this paper, but for the moment I wish to speak of the modus operandi of the discovery of these additions to the list of elements.

The discovery of argon came about in a rather singular way. Lord Rayleigh, of the Royal Institution, had noticed in experiments with nitrogen that when samples of this element were obtained from chemicals, such samples were uniformly about one per cent, lighter in weight than similar quantities of nitrogen obtained from the atmosphere. This discrepancy led him to believe that the atmospheric nitrogen must contain some impurity.

Curiously enough, the experiments of Cavendish, the discoverer of nitrogen—experiments made more than a century ago—had seemed to show quite conclusively that some gaseous substance different from nitrogen was to be found mixed with the samples of this gas as he obtained it from the atmosphere. This conclusion of Cavendish, put forward indeed but tentatively, had been quite ignored by his successors. Now, however, it transpired, by experiments made jointly by Lord Rayleigh and Professor Ramsay, that the conclusion was quite justified, it being shown presently that there actually exists in every portion of nitrogen, as extracted from the atmosphere, a certain quantity of another gas, hitherto unknown, and which now received the name of argon. It will be recalled with what astonishment the scientific and the unscientific world alike received the announcement made to the Royal Society in 1895 of the discovery of argon, and the proof that this hitherto unsuspected constituent of the atmosphere really constitutes about one per cent, of the bulk of atmospheric nitrogen, as previously estimated.

The discovery here on the earth of a substance which Professor Lockyer had detected as early as 1868 in the sun, and which he had provisionally named helium, excited almost equal interest; but this element was found in certain minerals, and not as a constituent of the atmosphere.

Having discovered so interesting a substance as argon, Professor Ramsay and his assistants naturally devoted much time and attention to elucidating the peculiarities of the new substance. In the course of these studies it became evident to them that the presence of argon alone did not fully account for all the phenomena they observed in handling liquefied air, and in 1898 Professor Ramsay was again able to electrify his audience at the Royal Society by the announcement of the discovery, in pretty rapid succession, of three other elementary substances as constituents of the atmosphere, these three being the ones just referred to—krypton, neon, and zenon.

It is a really thrilling experience, standing in the presence of the only portions of these new substances that have been isolated, to hear Professor Ramsay and Dr. Travers, his chief assistant, tell the story of the discovery—how they worked more and more eagerly as they found themselves, so to say, on a "warmer scent," following out this clew and that until the right one at last brought the chase to a successful issue. "It was on a Sabbath morning in June, if I remember rightly, when we finally ran zenon down," says Dr. Travers, with a half smile; and Professor Ramsay, his eyes twinkling at the recollection of this very unorthodox procedure, nods assent. "And have you got them all now?" I queried, after hearing the story. "Yes; we think so," replied Professor Ramsay. "And I am rather glad of it," he adds, with a half sigh, "for it was wearisome even though fascinating work." Just how wearisome it must have been only a professional scientific investigator can fully comprehend; but the fascination of it all may be comprehended in some measure by every one who has ever attempted creative work of whatever grade or in whatever field.

I have just said that the little test-tubes contain the only bit of each of the substances named that has ever been isolated. This statement might lead the untechnical reader to suppose that these substances, once isolated, have been carefully stored away and jealously guarded, each in its imprisoning test-tubes. Jealously guarded they have been, to be sure, but there has not been, by any means, the solitary confinement that the words might seem to imply. On the contrary, each little whiff of gas has been subjected to a variety of experiments—made to pass through torturing-tubes under varying conditions of temperature, and brought purposely in contact with various other substances, that its physical and chemical properties might be tested. But in each case the experiment ended with the return of the substance, as pure as before, to its proper tube. The precise results of all these experiments have been communicated to the Royal Society by Professor Ramsay. Most of these results are of a technical character, hardly appealing to the average reader. There is one very salient point, however, in regard to which all the new substances, including argon and helium, agree; and it is that each of them seems to be, so far as present experiments go, absolutely devoid of that fundamental chemical property, the power to combine with other elements. All of them are believed to be monatomic—that is to say, each of their molecules is composed of a single atom. This, however, is not an absolutely novel feature as compared with other terrestrial elements, for the same thing is true, for example, of such a familiar substance as mercury. But the incapacity to enter into chemical combinations seems very paradoxical; indeed it is almost like saying that these are chemical elements which lack the most fundamental of chemical properties.

It is this lack of combining power, of course, that explains the non-discovery of these elements during all these years, for the usual way of testing an element is to bring it in contact with other substances under conditions that permit its atoms to combine with other atoms to the formation of new substances. But in the case of new elements such experiments as this have not proved possible under any conditions as yet attained, and reliance must be had upon other physical tests—such as variation of the bulk of the gas under pressure, and under varying temperatures, and a study of the critical temperatures and pressures under which each gas becomes a liquid. The chief reliance, however, is the spectroscope—the instrument which revealed the presence of helium in the sun and the stars more than a quarter of a century before Professor Ramsay ferreted it out as a terrestrial element. Each whiff of colorless gas in its test-tube interferes with the light passing through it in such a way that when viewed through a prism it gives a spectrum of altogether unique lines, which stamp it as krypton, neon, or zenon as definitely as certain familiar and more tangible properties stamp the liquid which imprisons it as mercury.

QUERIES SUGGESTED BY THE NEW GASES

Suppose that a few years ago you had asked some chemist, "What are the constituents of the atmosphere?" He would have responded, with entire confidence, "Oxygen and nitrogen chiefly, with a certain amount of water-vapor and of carbonic-acid gas and a trace of ammonia." If questioned as to the chief properties of these constituents, he would have replied, with equal facility, that these are among the most important elements; that oxygen might almost be said to be the life-giving principle, inasmuch as no air-breathing creature could get along without it for many moments together; and that nitrogen is equally important to the organism, though in a different way, inasmuch as it is not taken up through the lungs. As to the water-vapor, that, of course, is a compound of oxygen and hydrogen, and no one need be told of its importance, as every one knows that water makes up the chief bulk of protoplasm; carbonic-acid gas is also a compound of oxygen, the other element this time being carbon, and it plays a quite different role in the economy of the living organism, inasmuch as it is produced by the breaking down of tissues, and must be constantly exhaled from the lungs to prevent the poisoning of the organism by its accumulation; while ammonia, which exists only in infinitesimal quantities in the air, is a compound of nitrogen and hydrogen, introducing, therefore, no new element.

If one studies somewhat attentively the relation which these elements composing the atmosphere bear to the living organism he cannot fail to be struck with it; and it would seem a safe inductive reasoning from the stand-point of the evolutionist that the constituents of the atmosphere have come to be all-essential to the living organism, precisely because all their components are universally present. But, on the other hand, if we consider the matter in the light of these researches regarding the new gases, it becomes clear that perhaps the last word has not been said on this subject; for here are four or five other elementary substances which, if far less abundant than oxygen and nitrogen, are no less widely distributed and universally present in the atmosphere, yet no one of which apparently takes any chemical share whatever in ministering to the needs of the living organism. This surely is an enigma.

Taking another point of view, let us try to imagine the real status of these new gases of the air. We think of argon as connected with nitrogen because in isolation experiments it remains after the oxygen has been exhausted, but in point of fact there is no such connection between argon and nitrogen in nature. The argon atom is just as closely in contact with the oxygen in the atmosphere as with the nitrogen; it simply repels each indiscriminately. But consider a little further; the argon atom not only repels all advance on the part of oxygen and nitrogen, but it equally holds itself aloof from its own particular kindred atoms. The oxygen or nitrogen atom never rests until it has sought out a fellow, but the argon atom declines all fellowship. When the chemist has played his tricks upon it, it finds itself crowded together with other atoms of the same kind; but lift up the little test-tube and these scurry off from one another in every direction, each losing its fellows forever as quickly as possible.

As one ponders this one is almost disposed to suggest that the atom of argon (or of krypton, helium, neon, or zenon, for the same thing applies to each and all of these) seems the most perfect thing known to us in the world, for it needs no companionship, it is self-sufficing. There is something sublime about this magnificient isolation, this splendid self-reliance, this undaunted and undauntable self-sufficiency—these are traits which the world is wont to ascribe to beings more than mortal. But let us pause lest we push too far into the old, discredited territory of metaphysics.

PROFESSOR J. J. THOMPSON AND THE NATURE OP ELECTRICITY

Many fascinating questions suggest themselves in connection with these strange, new elements—new, of course, only in the sense of human knowledge—which all these centuries have been about us, yet which have managed until now to keep themselves as invisible and as intangible as spirits. Have these celibate atoms remained thus always isolated, taking no part in world-building? Are they destined throughout the sweep of time to keep up this celibate existence? And why do these elements alone refuse all fellowship, while the atoms of all the other seventy-odd known elements seek out mates under proper conditions with unvarying avidity?

It is perhaps not possible fully to answer these questions as yet, but recent studies in somewhat divergent fields give us suggestive clews to some of them. I refer in particular to the studies in reference to the passage of electricity through liquids and gases and to the observations on radioactivity. The most conspicuous worker in the field of electricity is Professor J. J. Thompson, who for many years has had charge of the Cavendish laboratory at Cambridge. In briefly reviewing certain phases of his work we shall find ourselves brought into contact with some of the same problems raised by workers in the other fields of physics, and shall secure some very interesting bits of testimony as to the solution of questions already outlined.

The line of observation which has led to the most striking results has to do, as already suggested, with the conduction of electricity through liquids and gases. It has long been known that many liquids conduct electricity with relative facility. More recently it has been observed that a charge of electricity carried by any liquid bears a curious relation to the atomic composition of that liquid. If the atom in question is one of the sort that can combine with only a single other atom (that is to say, a monovalent atom), each atom conveys a unit charge, which is spoken of as an ion of electricity. But if a divalent atom is in question the charge carried is double, and, similarly, a trivalent atom carries a triple charge. As there are no intermediate charges it is obvious that here a very close relation is suggested between electrical units and the atomic units of matter.

This, however, is only a beginning. Far more interesting are the results obtained by the study of gases in their relation to the conduction of electricity. As is well known, gases under ordinary conditions are nonconductors. But there are various ways in which a gas may be changed so as to become a conductor; for example, by contact with incandescent metals or with flame, or by treating with ultra-violet light, with Rontgen rays, or with the rays of a radio-active substance. Now the all-important question is as to just what change has taken place in the gas so treated to make it a conductor of electricity. I cannot go into details here as to the studies that have been addressed to the answer of this question, but I will briefly epitomize what, for our present purpose, are the important results. First and foremost of these is the fact that a gas thus rendered conductive contains particles that can be filtered out of it by passing the gas through wool or through water. These particles are the actual agents of conduction of electricity, since the gas when filtered ceases to be conductive. But there is another way in which the particles may be removed—namely, by action of electricity itself. If the gas be caused to pass between two metal plates, one of them insulated and attached to an electrometer, a charge of positive electricity at high potential sent through the other plate will drive part of the particles against the insulated plate. This proves that the particles in question are positively electrified. The amount of the charge which they carry may be measured by the electrometer.

The aggregate amount of the electrical charge carried by these minute particles in the gas being known, it is obvious that could we know the number of particles involved the simplest calculation would determine the charge of each particle. Professor Thompson devised a singularly ingenious method of determining this number. The method was based on the fact discovered by C. T. R. Wilson that charged particles acted as nuclei round which small drops of water condense much as dust particles serve the same purpose. "In dust-free air," says Professor Thompson, "as Aitken showed, it is very difficult to get a fog when damp air is cooled, since there are no nuclei for the drops to condense round. If there are charged particles in dust-free air, however, the fog will be deposited round these by super-saturation far less than that required to produce any appreciable fog when no charged particles are present.

"Thus, in sufficiently supersaturated damp air a cloud is deposited on these charged particles and they are thus rendered visible. This is the first step towards counting them. The drops are, however, far too small and too numerous to be counted directly. We can, however, get their number indirectly as follows: suppose we have a number of these particles in dust-free air in a closed vessel, the air being saturated with water-vapor; suppose now that we produce a sudden expansion of the air in the vessel; this will cool the air, it will be supersaturated with vapor, and drops will be deposited round the charged particles. Now if we know the amount of expansion produced we can calculate the cooling of the gas, and, therefore, the amount of water deposited. Thus we know the volume of water in the form of drops, so that if we know the volume of one drop we can deduce the number of drops. To find the size of a drop, we make use of the investigations made by Sir George Stokes on the rate at which small spheres fall through the air. In consequence of the viscosity of the air small bodies fall exceedingly slowly, and the smaller they are the slower they fall." *

Professor Thompson gives us the formula by which Stokes made his calculation. It is a relatively simple algebraic one, but need not be repeated here. For us it suffices that with the aid of this formula, by merely measuring the actual descent of the top of a vapor cloud, Professor Thompson was able to find the volume of the drops and thence the number of particles. The number of particles being known, the charge of electricity carried by each could be determined, as already suggested. Experiments were made with air, hydrogen, and carbonic acid, and it was found that the particles had the same charge in all of these gases. "A strong argument," says Professor Thompson, "in favor of the atomic character of electricity." When we add that the charge in question was found to be the same as the unit charge of an ion in a liquid, it will be seen that the experiment has other points of interest and suggestiveness.

Even more interesting in some regards were the results of computation as to the actual masses of the charged particles in question. Professor Thompson found that the carrier of a negative charge could have only about one-thousandth part of the mass of a hydrogen atom, which latter had been regarded as the smallest mass able to have an independent existence. Professor Thompson gave the name corpuscle to these units of negative electricity; they are now more generally termed electrons. "These corpuscles," he says, "are the same however the electrification may have risen or wherever they may be found. Negative electricity in a gas at a low pressure has thus a structure analogous to that of a gas, the corpuscles taking the place of the molecules. The 'negative electric fluid,' to use the old notation, resembles the gaseous fluid with a corpuscular instead of a molecular structure.'" Professor Thompson does not hesitate to declare that we now "know more about 'electric fluid' than we know about such fluids as air or water."*3* The results of his studies lead him, he declares, "to a view of electrification which has a striking resemblance to that of Franklin's One Fluid Theory of Electricity. Instead of taking, as Franklin did, the electric fluid to be positive electricity," he says, "we take it to be negative. The 'electric fluid' of Franklin corresponds to an assemblage of corpuscles, negative electrification being a collection of these corpuscles. The transference of electrification from one place to another is effected by the motion of corpuscles from the place where there is a gain of positive electrification to the place where there is a gain of negative. A positively electrified body is one that has lost some of its corpuscles."*4* According to this view, then, electricity is not a form of energy but a form of matter; or, to be more precise, the electrical corpuscle is the fundamental structure out of which the atom of matter is built. This is a quite different view from that scarcely less recent one which regards electricity as the manifestation of ether strain, but it must be admitted that the corpuscular theory is supported by a marvellous array of experimental evidence, though it can perhaps hardly be claimed that this brings the theory to the plane of demonstration. But all roads of physical science of late years have seemed to lead towards the electron, as will be made further manifest when we consider the phenomena of radio-activity, to which we now turn.

RADIO-ACTIVITY

In 1896, something like a year after the discovery of the X-ray, Niewenglowski reported to the French Academy of Sciences that the well-known chemical compound calcium sulphide, when exposed to sunlight, gave off rays that penetrated black paper. He had made his examinations of this substance, since, like several others, it was known to exhibit strong fluorescent or phosphorescent effects when exposed to the cathode rays, which are known to be closely connected with the X-rays. This discovery was followed very shortly by confirmatory experiments made by Becquerel, Troost, and Arnold, and these were followed in turn by the discovery of Le Bon, made almost simultaneously, that certain bodies when acted upon by sunlight give out radiations which act upon a photographic plate. These manifestations, however, are not the effect of radio-activity, but are probably the effects of short ultra-violet light waves, and are not produced spontaneously by the substances. The radiations, or emanations, of the radio-active substances, on the other hand, are given out spontaneously, pass through substances opaque to ordinary light, such as metal plates, act upon photographic plates, and discharge electrified bodies. The substances uranium, thorium, polonium, radium, and their compounds are radioactive, radium being by far the most active.

The first definite discovery of such a radio-active substance was made by M. Henri Becquerel, in 1896, while making some experiments upon the peculiar ore pitch-blende. Pitch-blende is a heavy, black, pitchy-looking mineral, found principally at present in some parts of Saxony and Bohemia on the Continent, in Cornwall in Great Britain, and in Colorado in America. It is by no means a recently discovered mineral, having been for some years the source of uranium and its compounds, which, on account of their brilliant colors, have been used in dye-stuffs and some kinds of stained glass. It is a complex mineral, containing at least eight or ten elements, which can be separated from it only with great difficulty and by complicated chemical processes.

Becquerers discovery was brought about by a lucky accident, although, like so many other apparently accidental scientific discoveries, it was the outcome of a long series of scientific experiments all trending in the same direction. He had found that uranium, when exposed to the sun's rays, appeared to possess the property of absorbing them and of then acting upon a photographic plate. Since pitch-blende contained uranium, or uranium salts, he surmised that a somewhat similar result might be obtained with the ore itself. He therefore prepared a photographic plate wrapped in black paper, intending to attempt making an impression on the plate of some metal body interposed between it and the pitch-blende. For this purpose he had selected a key; but as the day proved to be cloudy he put the plate, with the key and pitch-blende resting upon it, in a dark drawer in his desk, and did not return to the experiment for several days. Upon doing so, however, he developed the plate without further exposure, when to his astonishment he found that the developed negative showed a distinct impression of the key. Clearly this was the manifestation of a property heretofore unknown in any natural substance, and was strikingly similar to the action of the Roentgen rays. Further investigations by Lord Kelvin, Beattie, Smolan, and Rutherford confirmed the fact that, like the Roentgen rays, the uranium rays not only acted upon the photographic plate but discharged electrified bodies. And what seemed the more wonderful was the fact that these "Becquerel rays," as they were now called, emanated spontaneously from the pitch-blende. But although this action is analogous to the Roentgen rays, at least as regards its action upon the photographic plate and its influence on the electric field, its action is extremely feeble in comparison, the Roentgen rays producing effects in minutes, or even seconds, which require days of exposure to uranium rays. The discovery of the radio-active properties of uranium was followed about two years later by the discovery that thorium, and the minerals containing thorium, possess properties similar to those of uranium. This discovery was made independently and at about the same time by Schmidt and Madame Skaldowska Curie. But the importance of this discovery was soon completely overshadowed by the discovery of radium by Madame Curie, working with her husband, Professor Pierre Curie, at the Ecole Polytechnique in Paris. Madame Curie, stimulated by her own discoveries and those of the other scientists just referred to, began a series of examinations upon various substances by numerous complicated methods to try and find a possible new element, as certain peculiarities of the substances found in the pitch-blende seemed to indicate the presence of some hitherto unknown body. The search proved a most difficult one on account of the peculiar nature of the object in question, but the tireless enthusiasm of Madame Curie knew nothing of insurmountable obstacles, and soon drew her husband into the search with her. Her first discovery was that of the substance polonium—so named by Madame Curie after her native country, Poland. This proved to be another of the radio-active substances, differing from any other yet discovered, but still not the sought-for element. In a short time, however, the two Curies made the great discovery of the element radium—a substance which, according to their estimate, is some one million eight hundred thousand times more radioactive than uranium. The name for this element, radium, was proposed by Madame Curie, who had also suggested the term "radio-activity."

The bearing of the discovery of radium and radioactivity upon theories of the atom and matter will be considered in a moment; first the more tangible qualities of this wonderful substance may be briefly referred to. The fact that radio-active emanations traverse all forms of matter to greater or less depth—that is, pass through wood and iron with something the same ease that light passes through a window-glass—makes the subject one of greatest interest; and particularly so as the demonstration of this fact is so tangible. While the rays given out by radium cannot, of course, be seen by the unaided eye, the effects of these rays upon certain substances, which they cause to phosphoresce, are strikingly shown. One of such substances is the diamond, and a most striking illustration of the power of radium in penetrating opaque substances has been made by Mr. George F. Kunz, of the American Museum of Natural History. Mr. Kunz describes this experiment as follows:

"Radium bromide of three hundred thousand activity was placed in a sealed glass tube inside a rubber thermometer-holder, which was tightly screwed to prevent any emanation of any kind from passing through the joints. This was placed under a heavy silver tureen fully one-sixteenth of an inch in thickness; upon this were placed four copper plates, such as are used for engraving; upon these a heavy graduated measuring-glass 10 cm. in diameter; this was filled with water to a depth of six inches. A diamond was suspended in the water and immediately phosphoresced. Whenever the tube of radium was drawn away more than two or three feet the phosphoresce ceased; whenever it was placed under the tureen the diamond immediately phosphoresced again. This experiment proves that the active power of the radium penetrated the following substances:

"Glass in the form of a tube, sealed at both ends; the rubber thermometer-holder; silver tureen; four copper plates; a glass vase or measuring-glass one-quarter of an inch in thickness; three inches of water. There is no previously known substance or agent, whether it be even light or electricity, that possesses such wonderfully penetrative powers."*5*

THE NATURE OF EMANATIONS FROM RADIO-ACTIVE BODIES

What, then, is the nature of these radiations? Are they actually material particles hurled through the ether? Or are they like light—and possibly the Roentgen rays—simply undulations in the ether? As yet this question is an open one, although several of the leading investigators have postulated tentative hypotheses which at least serve as a working basis until they are either confirmed or supplanted. On one point, however, there seems to be unanimity of opinion—there seems to be little question that there are at least three different kinds of rays produced by radio-active substances. According to Sir William Crookes, the first of these are free electrons, or matter in an ultra-gaseous state, as shown in the cathode stream. These particles are extremely minute. They carry a negative charge of electricity, and are identified with the electric corpuscles of Thompson. Rays of the second kind are comparable in size to the hydrogen atom, and are positively electrified. These are easily checked by material obstructions, although they render the air a conductor and affect photographic plates. The third are very penetrating rays, which are not deflected by electricity and which are seemingly identical with Roentgen rays. Professor E. Rutherford has named these rays beta (B), alpha (a), and gamma (v) rays respectively. Of these the beta rays are deviated strongly by the magnetic field, the alpha much less so—very slightly, in fact—while the gamma rays are not affected at all. The action of these three different sets of rays upon certain substances is not the same, the beta and gamma rays acting strongly upon barium platinocyanide, but feebly on Sidot's blende, while the alpha rays act exactly the reverse of this, acting strongly on Sidot's blende.

If a surface is coated with Sidot's blende and held near a piece of radium nitrate, the coated surface begins to glow. If now it is examined with a lens, brilliant sparks or points can be seen. As the radium is brought closer and closer these sparks increase in number, until, as Sir William Crookes says, we seem to be witnessing a bombardment of flying atoms hurled from the radium against the surface of the blende. A little instrument called a spinthariscope, devised by Dr. Crookes and on sale at the instrument and optical-goods shops, may be had for a trifling sum. It is fitted with a lens focused upon a bit of Sidot's blende and radium nitrate, and in a dark room shows these beautiful scintillations "like a shower of stars." A still less expensive but similar device is now made in the form of a microscopic slide, to be used with the ordinary lens.

As we said a moment ago, radium appears to be an elementary substance, as shown by its spark-spectrum being different from that of any other known substance—the determinative test as fixed by the International Chemical Congress. A particle of radium free from impurities should, therefore, according to the conventional conception of an element, remain unchanged and unchangeable. If any such change did actually take place it would mean that the conception of the Daltonian atom as the ultimate particle of matter is definitively challenged from a new direction. This is precisely what has taken place. In July of 1903 Sir William Ramsay and Mr. Soddy, in making some experiments with radium, saw produced, apparently from radium emanations, another quite different and distinct substance, the element helium. The report of such a revolutionary phenomenon was naturally made with scientific caution. Though the observation seemed to prove the actual transformation of one element into another, Professor Ramsay himself was by no means ready to declare the absolute certainty of this. Yet the presumption in favor of this interpretation of the observed phenomena is very strong; and so cautious a reasoner as Professor Rutherford has declared recently that "there can be no doubt that helium is derived from the emanations of radium in consequence of changes of some kind occurring in it."*6*

"In order to explain the presence of helium in radium on ordinary chemical lines," says Professor Rutherford, "it has been suggested that radium is not a true element, but a molecular compound of helium with some substance known or unknown. The helium compound gradually breaks down, giving rise to the helium observed. It is at once obvious that this postulated helium compound is of an entirely different character to any other compound previously observed in chemistry. Weight for weight, it emits during its change an amount of energy at least one million times greater than any molecular compound known. In addition, it must be supposed that the rate of breaking up of the helium compound is independent of great ranges of temperature—a result never before observed in any molecular change. The helium compound in its breaking up must give rise to the peculiar radiations and also pass through the successive radio-active change observed in radium.... On the other hand, radium, as far as it has been examined, has fulfilled every test required of an element. It has a well-marked and characteristic spectrum, and there is no reason to suppose that it is not an element in the ordinarily accepted sense of the term."*7*

THE SOURCE OF ENERGY OF RADIO-ACTIVITY

In 1903 Messrs. Curie and Laborde*8* made the remarkable announcement that a crystal of radium is persistently warmer than its surrounding medium; in other words, that it is perpetually giving out heat without apparently becoming cooler. At first blush this seemed to contradict the great physical law of the conservation of energy, but physicists were soon agreed that a less revolutionary explanation of the phenomenon is perfectly tenable. The giving off of heat is indeed only an additional evidence of the dissipation of energy to which the radio-active atom is subjected. And no one now believes that radio-activity can persist indefinitely without actually exhausting the substance of the atom. Even so, the evidence of so great a capacity to give out energy is startling, and has given rise to various theories (all as yet tentative) in explanation. Thus J. Perrin*9* has suggested that atoms may consist of parts not unlike a miniature planetary system, and in the atoms of the radio-elements the parts more distant from the centre are continually escaping from the central attraction, thus giving rise to the radiations. Monsieur and Madame Curie have suggested that the energy may be borrowed from the surrounding air in some way, the energy lost by the atom being instantly regained. Pilipo Re,*10* in 1903, advanced the theory that the various parts of the atom might at first have been free particles constituting an extremely tenuous nebula.

These parts gradually becoming collected around condensed centres have formed what we know as the atoms of elements, the atom thus becoming like an extinct sun of the solar system. From this point of view the radio-active atoms represent an intermediate stage between nebulae and chemical atoms, the process of contraction giving rise to the heat emissions.

Lord Kelvin has called attention to the fact that when two pieces of paper, one white and the other black, are placed in exactly similar glass vessels of water and exposed to light, the temperature of the vessel containing the black paper is raised slightly higher than the other. This suggests the idea that in a similar manner radium may keep its temperature higher than the surrounding air by the absorption of other radiations as yet unknown.

Professor J. J. Thompson believes that the source of energy is in the atom itself and not external to it. "The reason," he says, "which induces me to think that the source of the energy is in the atom of radium itself and not external to it is that the radio-activity of substances is in all cases in which we have been able to localize it a transient property. No substance goes on being radio-active very long. It may be asked, how can this statement be reconciled with the fact that thorium and radium keep up their activity without any appreciable falling off with time. The answer to this is that, as Rutherford and Soddy have shown in the case of thorium, it is only an exceedingly small fraction of the mass which is at any one time radio-active, and that this radio-active portion loses its activity in a few hours, and has to be replaced by a fresh supply from the non-radio-active thorium."*11*

If Professor Thompson's view be correct, the amount of potential energy inherent in the atom must be enormous.

RADIO-ACTIVITY AND THE STRUCTURE OF THE ATOM

But whatever the source of the energy displayed by the radio-active substances, it is pretty generally agreed that the radio-activity of the radio-elements results in the disruption of their atoms. Since all substances appear to be radio-active in a greater or less degree, it would seem that, unless there be a very general distribution of radio-active atoms throughout all substances, all atoms must be undergoing disruption. Since the distribution of radio-active matter throughout the earth is so great, however, it is as yet impossible to determine whether this may not account for the radio-activity of all substances.

As we have just seen, recent evidence seems to point to the cause of the disruption of radio-active atoms as lying in the atoms themselves. This view is quite in accord with modern ideas of the instability of certain atoms. It has been suggested that some atoms may undergo a slower disintegration without necessarily throwing off part of their systems with great velocity. It is even possible that all matter may be undergoing transformation, this transformation tending to simplify and render more stable the constituents of the earth. The radio-active bodies, however, are the only ones that have afforded an opportunity for studying this transformation. In these the rapidity of the change would be directly proportionate to their radioactivity. Radium, according to the recent estimate of the Curies, would be disintegrating over a million times more rapidly than uranium. Since the amount of transformation occurring in radium in a year amounts to from 1-2000 to 1-10,000 of the total amount, the time required for the complete transformation of an atom of uranium would be somewhere between two billion and ten billion years—figures quite beyond the range of human comprehension.

Various hypotheses have been postulated to account for the instability of the atom. Perhaps the most thinkable of these to persons not specially trained in dealing with abstruse subjects is that of Professor Thompson. It has the additional merit, also, of coming from one of the best-known investigators in this particular field. According to this hypothesis the atom may be considered as a mass of positively and negatively charged particles, all in rapid motion, their mutual forces holding them in equilibrium. In case of a very complex structure of this kind it is possible to conceive of certain particles acquiring sufficient kinetic energy to be projected from the system. Or the constraining forces may be neutralized momentarily, so that the particle is thrown off at the same velocity that it had acquired at the instant it is released. The primary cause of this disintegration of the atom may be due to electro-magnetic radiation causing loss of energy of the atomic system.

Sir Oliver Lodge suggests that this instability of the atom may be the result of the atom's radiation of energy. "Lodge considered the simple case of a negatively charged electron revolving round an atom of mass relatively large but having an equal positive charge and held in equilibrium by electrical forces. This system will radiate energy, and since the radiation of energy is equivalent to motion in a resisting medium, the particle tends to move towards the centre and its speed consequently increases. The rate of radiation of energy will increase rapidly with the speed of the electron. When the speed of the electron becomes very nearly equal to the velocity of light, according to Lodge, the system is unstable. It has been shown that the apparent mass of an electron increases very rapidly as the speed of light is approached, and is theoretically infinite at the speed of light. There will be at this stage a sudden increase of the mass of the revolving atom, and, on the supposition that this stage can be reached, a consequent disturbance of the balance of forces holding the system together. Lodge considers it probable that under these conditions the parts of the system will break asunder and escape from the sphere of one another's influence.

"It is probable," adds Rutherford, "that the primary cause of the disintegration of the atom must be looked for in the 1 ss of energy of the atomic system due to electro-magnetic radiation."*12*

Several methods have been devised for testing the amount of heat given off by radium and its compounds, and for determining its actual rise in temperature above that of the surrounding atmosphere. One of these methods is to place some substance, such as barium chloride, in a calorimeter, noting at what point the mercury remains stationary. Radium is then introduced, whereupon the mercury in the tube gradually rises, falling again when the radium is removed. By careful tests it has been determined that a gram of radium emits about twenty-four hundred gram-calories in twenty-four hours. On this basis a gram of radium in a year emits enough energy to dissociate about two hundred and twenty-five grams of water.

What seems most remarkable about this constant emission of heat by the radium atom is that it does not apparently draw upon external sources for it, but maintains it by the internal energy of the atom itself. This latent energy must be enormous, but is only manifested when the atom is breaking up. In this process of disruption many of the particles are thrown off; but the greater part seem to be stopped in their flight in the radium itself, so that their energy of motion is manifested in the form of heat. Thus, if this explanation is correct, the temperature of the radium is maintained above that of surrounding substances by the bombardment of its own particles. Since the earth and the atmosphere contain appreciable quantities of radio-active matter, this must play a very important part in determining the temperature of the globe—so important a part, indeed, that all former estimates as to the probable length of time during which the earth and sun will continue to radiate heat are invalidated. Such estimates, for example, as that of Lord Kelvin as to the probable heat-giving life of the sun must now be multiplied from fifty to five hundred times.

In like manner the length of time that the earth has been sufficiently cool to support animal and vegetable life must be re-estimated. Until the discovery of radium it seemed definitely determined that the earth was gradually cooling, and would continue to cool, un til, like the moon, it would become too cold to support any kind of vegetable or animal life whatever. But recent estimates of the amount of radio-active matter in the earth and atmosphere, and the amount of heat constantly given off from this source, seem to indicate that the loss of heat is (for the moment) about evenly balanced by the heat given out by radio-active matter. Thus at the beginning of the new century we see the phenomenon of a single discovery in science completely overturning certain carefully worked out calculations, although not changing the great principles involved. It is but the repetition of the revolutionary changes that occur at intervals in the history of science, a simple discovery setting at naught some of the most careful calculations of a generation.



V. THE MARINE BIOLOGICAL LABORATORY AT NAPLES

THE AQUARIUM

MANY tourists who have gone to Naples within recent years will recall their visit to the aquarium there among their most pleasant experiences. It is, indeed, a place worth seeing. Any Neapolitan will direct you to the beautiful white building which it occupies in the public park close by the water's side. The park itself, statue-guarded and palm-studded, is one of the show-places of the city; and the aquarium building, standing isolated near its centre, is worthy of its surroundings. As seen from the bay, it gleams white amid the half-tropical foliage, with the circling rampart of hills, flanked by Vesuvius itself, for background. And near at hand the picturesque cactus growth scrambling over the walls gives precisely the necessary finish to the otherwise rather severe type of the architecture. The ensemble prepares one to be pleased with whatever the structure may have to show within.

It prepares one also, though in quite another way, for a surprise; for when one has crossed the threshold and narrow vestibule, while the gleam of the outside brightness still glows before his eyes, he is plunged suddenly into what seems at first glimpse a cavern of Egyptian darkness, and the contrast is nothing less than startling. To add to the effect, one sees all about him, near the walls of the cavern, weird forms of moving creatures, which seem to be floating about lazily in the air, in grottos which glow with a dim light or sparkle with varied colors. One is really looking through glass walls into tanks of water filled with marine life; but both glass and water are so transparent that it is difficult at first glimpse to realize their presence, unless a stream of water, with its attendant bubbles, is playing into the tanks. And even then the effect is most elusive; for the surface of the water, which you are looking up to from below, mirrors the contents of the tanks so perfectly that it is difficult to tell where the reality ends and the image begins, were it not that the duplicated creatures move about with their backs downward in a scene all topsy-turvy. The effect is most fantastic.