A History of Science Volume V Part 4

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 pa.s.sing 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 pa.s.s 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 ma.s.ses 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 ma.s.s of a hydrogen atom, which latter had been regarded as the smallest ma.s.s 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 a.n.a.logous 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 a.s.semblage 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 phosph.o.r.escent 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, pa.s.s 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 princ.i.p.ally 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 gla.s.s. 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 a.n.a.logous 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, pa.s.s through wood and iron with something the same ease that light pa.s.ses through a window-gla.s.s--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 phosph.o.r.esce, are strikingly shown. One of such substances is the diamond, and a most striking ill.u.s.tration 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 gla.s.s tube inside a rubber thermometer-holder, which was tightly screwed to prevent any emanation of any kind from pa.s.sing 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-gla.s.s 10 cm. in diameter; this was filled with water to a depth of six inches.

A diamond was suspended in the water and immediately phosph.o.r.esced.

Whenever the tube of radium was drawn away more than two or three feet the phosph.o.r.esce ceased; whenever it was placed under the tureen the diamond immediately phosph.o.r.esced again. This experiment proves that the active power of the radium penetrated the following substances:

"Gla.s.s in the form of a tube, sealed at both ends; the rubber thermometer-holder; silver tureen; four copper plates; a gla.s.s vase or measuring-gla.s.s 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 pa.s.s 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 const.i.tuting 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 gla.s.s 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 ma.s.s 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 const.i.tuents 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 ma.s.s 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 ma.s.s 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 ma.s.s 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 ma.s.s 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 quant.i.ties 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 repet.i.tion 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 gla.s.s walls into tanks of water filled with marine life; but both gla.s.s 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.

More than that, it is most beautiful as well. You are, in effect, at the bottom of the ocean--or rather, at the bottom of many oceans in one. No light comes to you except through the grottos about you--grottos haunted by weird forms of the deep, from graceful to grotesque, from almost colorless to gaudy-hued. To your dilated pupils the light itself has the weird glow of unreality. It is all like the wonders of the Arabian Nights made tangible or like a strange spectacular dream. If one were in a great diving-bell at the bottom of the veritable ocean he could hardly feel more detached from the ordinary aerial world of fact.

As one recovers his senses and begins to take definite note of things about him he sees that each one of the many grottos has a different set of occupants, and that not all of the creatures there are as unfamiliar as at first they seemed. Many of the fishes, for example, and the lobsters, crabs, and the like, are familiar enough under other conditions, but even these old acquaintances look strange under these changed circ.u.mstances. But for the rest there are mult.i.tudes of forms that one had never seen or imagined, for the sea hides a myriad of wonders which we who sail over its surface, and at most glance dimly a few feet into its depths, hardly dream of. Even though one has seen these strange creatures "preserved" in museums, he does not know them, for the alleged preservation there has retained little enough of essential facies of the real creature, which the dead sh.e.l.l can no more than vaguely suggest.

Here, however, we see the real thing. Each creature lives and moves in a habitat as nearly as may be like that which it haunted when at liberty, save that tribes that live at enmity with one another are here separated, so that the active struggle for existence, which plays so large a part in the wild life of sea as well as land, is not represented. For the rest the creatures of the deep are at home in these artificial grottos, and disport themselves as if they desired no other residence. For the most part they pay no heed whatever to the human inspectors without their homelike prisons, so one may watch their activities under the most favorable conditions.

It is odd to notice how curiously sinuous are all the movements, not alone of the fish, but of a large proportion of the other forms of moving life of the waters. The curve, the line of beauty, is the symbol of their every act; there are no angles in their world. They glide hither and yon, seemingly without an effort, and always with wavy, oscillating gracefulness. The acme of this sinuosity of movement is reached with those long-drawn-out fishes the eels. Of these there are two gigantic species represented here--the conger, a dark-skinned, rather ill-favored fellow, and the beautiful Italian eel, with a velvety, leopard-spotted skin. These creatures are gracefulness itself.