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 s.p.a.ce, where something approaching the zero temperature is supposed to prevail, also contradicts this a.s.sumption. 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 a.s.sumes 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. .h.i.therto 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 a.s.sert themselves in unwonted measure seems clearly forecast in the phenomena of increased magnetism, and of phosph.o.r.escence 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 Inst.i.tution 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 inst.i.tutions, but in no case, perhaps, is the contrast more striking between the exterior appearance of a famous scientific inst.i.tution 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 a.s.sociation 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 mult.i.tudinous 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 a.s.sociation 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 quant.i.ties 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 pa.s.sed 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 acc.u.mulated 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 pa.s.s 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 pa.s.sing through gradual stages of cooling until their light dies out altogether. Very recently Professor Lockyer has been enabled, through utilization of the multiform records acc.u.mulated during years of study, to define the various typical stages of the sidereal evolution; and not merely to define them but to ill.u.s.trate 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 a.n.a.logy, 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 a.s.sumed a red color as it cooled, pa.s.sing 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 s.p.a.ce 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 ma.s.ses, 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 ma.s.s 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 cla.s.sical. Interiorly it is like so many other European inst.i.tutions 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--gla.s.s 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 gla.s.s 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 const.i.tuents 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 Inst.i.tution, 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 quant.i.ties 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 quant.i.ty 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. .h.i.therto unsuspected const.i.tuent of the atmosphere really const.i.tutes 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 const.i.tuent of the atmosphere.

Having discovered so interesting a substance as argon, Professor Ramsay and his a.s.sistants 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 const.i.tuents 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 a.s.sistant, 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 a.s.sent. "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 pa.s.s 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 pa.s.sing 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 const.i.tuents 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 const.i.tuents, 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 acc.u.mulation; while ammonia, which exists only in infinitesimal quant.i.ties 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 const.i.tuents 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 pa.s.sage 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.