SOME years ago, a club of specialists in Cambridge, stirred by a remark of one of its members, that when we look deeply into any scientific subject we are dismayed at the lack of exactness in most of our cherished scientific beliefs, fell to discussing, “What is surely known? ”
The biologist confessed that in his subject there is no fundamental theory which is established beyond question. How fertilization really takes place, the beginning of life, is a much - mooted point; there may be double fertilization where there is apparently only single fertilization. The theory of heredity has great exceptions and contradictions, Protoplasm is the veil which hides life from us. The chemist does not know the shape of his atoms, and is not sure that the so-called elements are truly elements. Gold, for instance, may consist of many elements ; there are scores of mysterious lines in the spectrum of its vapor. The very unit of measure of the chemist, the hydrogen atom, formerly supposed to be one and indivisible, is now, as we shall show in this paper with a good array of reason, a composite structure and not indivisible. It also has a complicated spectrum in the region which is veiled to our eyes, but is now revealed in the invisible violet by the labors of the physicist. The geologist has no definite period of years by which he can estimate with accuracy the age of the earth. The centre of the earth may be solid or it may be liquid. When the physicist’s turn came to take part in the discussion, he claimed for his science the possession of the one absolute and incontrovertible basis of all future theories, — the fact of the to-and-fro or periodic motion of radiant energy.
The fact that light and all radiant energy consists of a to-and-fro motion, with perfectly measurable wave lengths, is the one fact which we know beyond question; the wave length of hydrogen is the same in the light which comes to us from a star five hundred million miles away as in the light of the gas contained in glass tubes in our laboratories. This light comes through space with a vibrating motion which was given to it where and when it was generated. The to-and-fro motion changes instantly at points in space infinitely near each other, so that we can think of this motion in all directions about a point, successively taking place in all possible angles or azimuths. This toand - fro motion holds throughout the universe; it is measured in the light of stars which are so distant that they cannot be seen. We have reason for thinking that the law of gravitation may not hold in the regions from which this light comes in its unalterable fashion. It was confessed at the club, after some argument, that the physicist had indeed a bit of absolute truth, — something which was the same through the universe as we see it, and something which could be measured with a marvelous degree of accuracy.
The great Maxwellian theory of the electro-magnetic nature of this to-and-fro motion has been considered, until lately, in what may be termed its large aspect; that is, the motions of the ether were calculated without reference to the motions of extremely small particles of matter, — much as if we should fix our minds on the motion of ocean waves, and disregard the ripples produced in the water by rapidly moving fishes. There were inconsistencies in the theory which could not be reconciled until we took into account the motions of the smallest particles of matter. The study of the infinitely small has therefore become of the first consideration, and has received its greatest impetus from the subject of electrical discharges. Maxwell, indeed, seems to have had a suspicion that much would be revealed in the subject of electricity by an investigation of such discharges; for he speaks of the desirability of it, in his great work. While the patient study of this most puzzling subject was being prosecuted, — a study which was derided by many as being of little importance, — Hertz succeeded in showing, experimentally, the wave motions of electricity, and thus in substantiating Maxwell’s hypothesis. He showed that the electric waves could be reflected, refracted, and polarized, and in short were identical in their nature with lightwaves. He produced the waves by means of electric sparks. These Hertz waves are used in wireless telegraphy. Such waves are in general at least two or three feet long. They have been produced one eighth of an inch long. The many puzzling manifestations of light produced by electric discharges in rarefied gases were undoubtedly to - and - fro motions in the ether, and had wave lengths; but some of these wave lengths were too small to be estimated. There were, for instance, beams of light which were shot forth at a large angle with the general direction of the electric discharge. Professor Crookes attributed this light — which was called, from its place of origin, the kathode light — to small particles which were shot off from the kathode, or negative terminal of the electric circuit. Many physicists did not agree with him in this conjecture. The passage of electricity through conducting liquids exhibited phenomena analogous to the discharges through gases; they could best be explained by the hypothesis that there were in all liquids wandering ions or small particles of matter which carried electric charges. When this idea seized the minds of investigators, the progress in building up the new hypothesis upon which the entire scientific world is now working became rapid. The solution of every substance is conceived to consist of free and bound ions. Even a solution of sugar resembles a gas in consisting of molecules which by their movement exert a pressure on the walls of the tumbler containing the solution. The passage of electricity through such a solution results in the separation of the molecules into active and passive. The active ions carry the electricity. Every solution, therefore, under the effect of an electric current, is like a beehive filled with drones and workers.
It was soon realized that such discharges through gases resembled the phenomena of the passage of electricity through solutions ; there were active and passive ions. Maxwell’s hypothesis was reinvestigated from the point of view of the possible magnetic effect of rapidly moving extremely small particles of matter carrying electric charges; and it was seen that where Maxwell’s large hypothesis failed to be upheld by facts, the theory of the magnetic effect of small particles carrying electric charges led to a more consistent view of the action of electricity. It was necessary to study the small undulations in the ether produced by the rapid motion and the impact of these particles; in other words, the motion of the small fishes in the large waves became all-important. It seemed as if we were returning to a corpuscular theory of light, or rather, to a combination of this hypothesis with the undulatory theory; we were coming also to the conception of a motion from particle to particle, and were strengthening our conviction that there was no such thing as action at a distance. We were forming a picture of waves started in the ether by the blows of very small charged bodies, called electrons, which moved with a velocity of many thousand miles a second, and which, by their impact against solid bodies, sent out waves which we can picture to ourselves as similar to the waves excited in the air by the impact of a projectile against a plate or the fall of a stone into water. I have said that Professor Crookes early entertained the belief that the peculiar kathode light which was the precursor of the X rays was due to the impact of rapidly moving particles ; and Weber, a German physicist, had elaborated a mathematical theory of electricity on the basis of the movement of small particles of charged matter. In this theory it was supposed that the positive and negative particles had the same velocity. This theory, however, could not be upheld without serious doubts. The modern theory, which is now the prevailing one, supposes that the negatively charged particle has the greatest motion, and that there are not equal quantities of positive and negative electricity passing in opposite directions when an electric current flows. By this hypothesis, it was predicted that the light of sodium vapor, the light which is produced when common salt is burned in a flame, when generated between the poles of a powerful electro-magnet would manifest certain optical peculiarities. The observer would see a doubling or a tripling of the yellow lines characteristic of the vapor of this salt. This theoretical conclusion was soon confirmed by observation, and it became possible to measure the size of the vibrating negative atom. It was found that it was only one thousandth of the chemist’s atom.
Then came the discovery of the X rays, and by means of the phenomena exhibited by them Professor Thomson arrived at another estimate of the size of the negative atom, which agreed fairly well with the estimate formed from the preceding method. We have now a conception of a particle of matter called an electron, which is the one thousandth part of the chemist’s atom, and which moves with a velocity approximating to that of light; its impact upon solid bodies generates waves in the ether which are called electromagnetic and which constitute light and heat. The positive atom is apparently inert electrically until the negative ion which we now call the electron has become detached from it. The positive atom can be called the drone in the electrical hive, and the electron the worker.
Since we have arrived at the conception of activity and passivity, cannot we suppose that the mass of bodies is not real, and is merely apparent; moreover, that the attraction of gravitation is an electrical phenomenon ?
How large, then, is this electron ? We have estimated it as the one thousandth part of the chemist’s atom. It has been computed that in a cubic inch of air — the volume represented by a small bird’s egg — the number of molecules is one followed by twenty-four ciphers. It conveys little idea to express this number in words. The hydrogen molecule is supposed by the chemist to consist of two atoms; and the physicist believes that each of these atoms has attached to it an electron which is one thousandth of the hydrogen atom. Tbe most powerful microscope of to-day can barely separate lines which are one hundred thousandth of an inch apart; yet a molecule of hydrogen (not an atom or an electron, — a fairly immense body in comparison with either) has a diameter of about one two hundred and fifty thousand millionths of an inch. The electron stands in relation to the bacilli, which have been revealed by the improvements in the modern microscope, much as the bacilli stand in relation to the size of the earth. This conception of the wandering ion has grown up from a study of the phenomena observed in the passage of electricity through liquids; the phenomena presented are called electrolytic. Water, for instance, breaks up, under the effect of the passage of electricity, into its gaseous components, oxygen and hydrogen; the hydrogen appears at the point where the electricity leaves the liquid, — that is, the negative terminal. There is an important question now agitating the municipal authorities of Cambridge in regard to the electrolytic action of the current of the trolley roads on the iron mains of the water supply. It has just been discovered that the pipes of one of the chief mains — that leading through Boylston Street and by the Soldier’s Field — are being badly eaten by this electrolytic action. The oxygen which is set free at the point where the current passes through the ground to the iron pipes oxidizes the metal by an action similar to that which we observe in our tinned water cans. This corroding action can be reduced by making the current leave the earth by the iron pipes at certain suitable points, instead of entering the pipes from the ground; in other words, generating at such points hydrogen instead of oxygen.
One sees, in traveling in Germany and in Switzerland, immense manufactories, or Fabriken, where electricity generated by water power is used to produce electrolytic action to form soda and potash and to reduce metals. Provided thus with many important facts drawn from a study of electrolysis in liquids, the physicist turned to a critical study of the perplexing phenomena presented by the passage of electricity through rarefied gases. One type of such phenomena is presented to us in the northern lights, and another type in lightning discharges. It was soon surmised that there was something analogous to electrolysis in these discharges. My late investigation of the effect of powerful discharges of electricity through gases has led me to many exemplifications of this electrolytic action. When, for instance, a strong current is passed between two large copper terminals in rarefied aqueous vapor, a brilliant copper mirror is formed on the glass containing vessel at the negative terminal, — that is, where the current leaves the copper, — and an oxide of copper is deposited at the point where it enters the copper. Thus oxygen is generated at this latter point, and hydrogen at the negative terminal, just as in the case of the Cambridge water pipes to which I have referred.
My experiments also lead me to the belief that all discharges of electricity through gases depend upon the existence of a certain amount of aqueous vapor in the gas; in other words, upon the possibility of an electrolytic action. In fact, a study of this electrolytic action of electricity has laid the foundations of a new branch of science, that of physical chemistry, which promises to be one of the most important sciences in the world. It brings the chemist and the physicist, the physiologist and the leader in sanitary science, closely together.
One of the most striking results of the theory of the electron is the discovery of the relationship of obscure phenomena which apparently stood far apart. We are familiar with the light emitted by phosphorus and by decaying matter. Almost all substances can be made to exhibit phosphorescent light by exposure to the sun. After this exposure, many of the sulphides of lime, and particularly the salts of barium, glow brilliantly in the dark. One can photograph by this phosphorescent light; but the light is entirely cut off or shielded from the photographic plate by a sheet of cardboard or a sheet of aluminium. It has been discovered that certain salts of barium, and other obscure salts obtained principally from pitchblende, emit a light which is related to ordinary phosphorescence. This new light has the remarkable property of being able to pass through thick cardboard and thin sheets of aluminium. One can obtain a photograph of the hand on a dry plate which is shielded from the hand by an opaque covering of paper or wood. The light resembles in every way the X-ray light, since we conceive the X-ray light to be excited by the impact of minute particles charged with electricity. We conclude that this new cousinship to phosphorescence is also a manifestation of the impact of electrons which are released from these new substances The impact causes ripples or waves in the ether.
I remember that in the year 1860 a man who occupied himself with a microscope was smiled at, as a blear-eyed, narrow specialist, who had little interest in the large affairs of humanity, — in the important questions of the time, such as the anti-slavery cause, the question of the Turk, the problems of free trade and the tariff. It was supposed that the microscope was a perfected instrument, and that little more could be done with it than to study the lower forms of life, which were interesting to the naturalist, but had remote relations with humanity. At that time the death rate in diphtheria was over sixty per cent, and more than five per cent of women died in childbirth. To-day, owing to improvements in the microscope, the death rate in diphtheria has been reduced to less than ten per cent, and the mortality in lying-in cases to one twentieth of one per cent.
By means of an appropriation from the German government, Zeiss has perfected microscope lenses which have made possible the study of bacilli, and have led to most important results in the treatment of disease. Modern aseptic surgery is also the result of investigations with this new instrument of research. Thus the improvements in the microscope have led to the germ theory of disease, the discovery of antitoxin, and to that greatest boon to mankind, the realization of the importance of aseptic surgery. In aseptic surgery the endeavor of the surgeon is to exclude the small germs which vitiate the blood, and the result of the study of electric discharges is now leading to methods of communicating electrons to the tissues or of setting them free. Violet light can set free electrons from metals; X rays can do the same. Moreover, the latter can burn the tissues, setting up some yet obscure form of electrolytic action. It is claimed strenuously by good authorities that there is a healing action in malignant skin diseases, due to this new electrical radiation. It is also claimed that the new radiation can aid, or in certain cases retard, the germination of seeds.
The science of physical chemistry has received its greatest impulse from the study of the dissociation effects resulting from the application of electricity on what may be termed a large scale; that is, by the employment of strong currents, such as are used in metallurgical operations and in the electrical furnace. A new branch of physical chemistry has lately been developed from the study of the infinitely little, which promises to be the most important science of the future; for it deals most intimately with the problems of life. This subject is called electro-chemistry. It is based upon the effect of electricity in revealing the important reactions and motions of the smallest particles of matter. The literature on this subject in current periodicals already exceeds that of any other department of physical science. Until a comparatively late day, heat and light were considered the principal agents which chemists employed to study the reactions of matter. In the new subject of electro-chemistry, electricity occupies the first place, as a destroyer and a readjuster; and heat and light are merely subordinate parts of its manifestations, differing from it only in length of waves in the ether. The to-and-fro motion, which is our incontestable fact, is an electrical vibration. When we consider the investigations in electro-chemistry, we perceive that the most important actions of electricity are not those we are conscious of in their great practical applications; it is rather in subtle and silent effects that it works its greatest changes on life and matter.
For the purpose of illustrating the manner in which electricity can reveal to the eye the motions of the infinitely small, I will speak again of the manifestation of lightning. Before a lightning flash occurs the air is colorless and invisible. We cannot distinguish its components, — oxygen, hydrogen, argon, neon, and possibly many other gases which it contains. When, however, the flash occurs, that which was without color becomes blinding white with suggestions of red, yellow, and blue. If we look through a prism of glass at the flash, we see a multitude of bright lines of many colors. These colors indicate the rate of movement of infinitely small particles or ions, which reveal themselves only under the stimulus of electricity. When the flash dies out they become again invisible, having recorded their wave lengths by the aid of electricity in agitating the small particles of silver on a photographic plate.
It seems to be evident that there is a path of human inquiry which leads somewhere into the open: that path is one into the world of the infinitely little. The hope of the world lies, I am convinced, in the labors of the physicist along this path. In 1860 the physicists were trying to comprehend and to measure large things. They were weighing the earth, estimating the distance of the heavenly bodies, or speculating on the limits of the stellar universe. There were measurements, too, of what was considered the velocity of electricity, which, however, was not this velocity. It was a large thing, and was therefore considered of importance in comparison with observations with a microscope. Men were thinking of large relations in the universe. Tyndall expressed the growing conviction of his time that light and heat differed from each other only in the length of ether waves, and struck a popular note in his treatise entitled Heat as a Mode of Motion. This book dealt with what seemed vast problems in the conservation of energy. Electricity was referred to only as a powerful means of producing light and heat; there was no intimation that light might be an electro-magnetic phenomenon. The world was impressed with thoughts of the equivalence between heat and work, but it was not yet ready for the theory that heat is an electric phenomenon. It had reason to feel proud of the generalization that heat and light are due to a to-and-fro motion in some medium pervading all space, which is provisionally called the ether, and that heat differs from light only in the length of wave. In 1873 Maxwell enunciated his celebrated hypothesis that light and heat are electro-magnetic in their nature. This theory is the leading one to-day in the physical world: it connects in close relationship phenomena which had never before been joined. However this hypothesis may be modified, we have in it a bit of knowledge of which I think we have reason to be proud. It is a kernel of absolute truth, — perhaps the only such kernel in the material world.