# Popular Science Monthly/Volume 67/July 1905/The Science Problems of the Twentieth Century

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* THE SCIENCE PROBLEMS OF THE TWENTIETH CENTURY.
By Professor A. E. DOLBEAR,
TUFTS COLLEGE.
LET us define science as knowledge of the relations of phenomena, and define phenomena as any or all changes that take place, which may be known to mankind. Let us also assume uniformity of action, that is that under assigned conditions the same phenomenon will be reproduced, what is called and what is meant by the term law.
We have several bodies of correlated relations which constitute such sciences as astronomy, chemistry, biology and so on. The phenomena exhibited by large bodies at great distances apart we call astronomy. Such as are exhibited by minute bodies near together we call chemistry, and the phenomena among living as distinguished from what we call dead things, we call biology. Among these and other similar sciences, where we have noted the uniformities in the phenomena and find ourselves able to predict occurrences, we say we have definite knowledge, and especially so when the bodies that exhibit the changes are of such magnitude that we may control them. This is what is meant by experimentation. Until phenomena are studied in their relations to other known and established relations they can not be said to be a corporate part of science. There are many isolated facts not yet in established relations, awaiting their proper setting. Facts are always scientific data, they are not science itself. That a body left unsupported will fall to the ground has been known for thousands of years, also that the moon revolves about the earth. The correlation that shows that both belong to the same class and are due to the same agency, gravitation, is science. The man who proved the relation was a scientific man, was doing scientific work. In like manner everybody has known in all times, of mankind and animals on the earth. The correlations that show their relationship is science, and the one who showed it was a scientific man. The two examples are to show that scientific work consists in establishing the relations among: phenomena. This is what marks the profound difference between the work of the nineteenth century and all the preceding ones—the establishment of the relations among phenomena.
Prior to the nineteenth century there was a vicious assumption underlying nearly all effort in the domain of knowledge, that was, that there were no necessary relations among the different classes of ​phenomena. That astronomy, geology, physics, chemistry, physiology and all the rest were independent departments of knowledge and that each could be worked out completely without help or hindrance from others. The great contributions of the nineteenth century showed they were all of one family, and the surprise as one after another were thus linked was only paralleled by the hostility manifested in many quarters to such a claim. Together they show strongly that the knowledge was so unexpected and so new that it was not easily assimilated. Especially was this true when the new implications made it needful to abandon much in philosophy and religion that had been held to be unassailable. Many heated battles were fought, but science was always victorious and never had to surrender a field once entered.
What these triumphs were has often been presented within a year or two, and the recital of them has raised the query in many minds whether there can possibly be left much of importance to be discovered. Alexander conquered the world and wept because there was no more Alexandrine work to do. He must go home and mope the rest of his life. Inactivity is an intolerable idea to an energetic man with but one idea. Heaven saved Alexander from a long endurance of such idleness as he feared, by removing him when his work was done.
Is there no more work for the man of science? Are there no more problems of importance awaiting the investigator? Have we all the knowledge we are likely to get? There are some who, having noted the prodigious product of the nineteenth century, have half feared that science has been worked out.
That this is not true I will endeavor to show.
Beginning with astronomy. We are well assured now that the earth as a part of the solar system has had a long history. That all these bodies have reached their present conditions and relations by a process of growth taking millions of years. The same factors that have been active in the past are still operative, producing changes in magnitude, in distances, in temperature and the like. The moon, once a corporate part of the earth, has left it through tidal action and will move still farther away for something like fifty millions of years, after which it will return. The sun is a mass of gas, which by its contraction through gravitation has become exceedingly hot, and is radiating its energy away at a definite and known rate. As it is limited in size and amount of material, one may without difficulty calculate that the supply of heat from it will last about ten millions of years. It will cease to shine and become cold unless something like a catastrophe shall reendow it with high temperature and larger volume, when it may repeat the history of these millions of years past. The same conditions of contraction and rise in temperature are observable in ​thousands of the heavenly bodies, and in all stages from thin gaseous masses to cold non-luminous solid bodies.
Now that we know so much of the past history of the solar system, and in addition that our nearest neighbor is more than 200,000 times the distance to the sun, also that the whole system is itself moving in space at the rate of about 400 millions of miles a year in the direction of the star Vega, we yet need to know whether this motion is a drift or part of an orbit. At present no one knows. The directions and rates of motion of a number of stars have been very well determined, but such measures are not numerous enough to enable us to say whether there is more order in the movements of stars than there is among the molecules of a gas, where molecular collisions are constantly taking place. Such phenomena as that of the new star which suddenly blazed out in Perseus are now explained only by assuming stellar collisions wherein the masses are so large and have such velocity that impact at once reduces them to incandescent gas. This means the possibility of such disaster to the solar system, but it is a present comfort to know that if we were to collide with our nearest neighbor at present rate, 12 miles a second, it will take nearly 50,000 years to reach it.
We have now about a hundred million stars in sight, and astronomers have been surprised that a greater number of the more remote ones are not to be seen. The actual number of stars in our universe is much smaller than had been supposed, and instead of there being an infinite number in an infinite space the present outlook is that there is a boundary to the visible universe; but this remains to be determined, and this problem is engaging attention in several of the great observatories. We all want to know what kind of a universe we live in and the series of events that take place in it. In older times there were supposed to be but seven members of the solar system. The nineteenth century discovered more than five hundred. Eros was discovered only six or eight years ago, while additional moons to both Jupiter and Saturn were seen for the first time within ten years. It is not probable that all have been discovered. Search is yet being made for other planets.
Though limited, one can get some idea of the magnitude of the universe when it appears that some of the remote stars are so far away as to require something like a million years for their light to reach us, though light travels at the rate of 186,000 miles a second—a distance so great that it would take trillions of years to reach them at the rate that we now are moving in space, namely about 400 millions of miles a year. Space seems illimitable, time is long, and if matter be indestructible, yet the solar system as we know it will have gone through all its phases of growth, maturity, old age and death, long enough before the general aspect of the heavens will have been greatly changed ​from what they are to-day. This is astronomical work of importance awaiting research.
We desire to know much more concerning the individual planets. Even-body asks, 'Are the planets inhabited?' and no favorable answer has yet been given. If one means by the question, inhabited by such beings as we are structurally, then one can say that if one of us were transported to any of the planets we could not live there a minute. Some, like Jupiter, are too hot; others, like the moon, too cold, or without air to breathe or water to drink, or with too great or too little gravity for our bodies. One does not need to assume such likeness, especially since we know something of the past history of man and animals on the earth, adapted to it in form, size, structure, habits and intelligence all correlated. To assume intelligence of our type is hardly allowable any more than for structures like ours. Vertebrate skeletons are not necessarily the only form in which intelligence of high type may abide. The implements and skill of the astronomers are yet to determine what can be learned about this question. Taking what we know about the development of life on earth, it would seem to be insanely improbable that among the millions of millions of huge bodies in the universe, all apparently made of the same kinds of matter and subject to the same laws, that the earth is the only one among them all to have life and mind developed upon it. But at present we do not know that it may not be true. Let the twentieth century find out.
Geology: The whole of geology was a gift of the nineteenth century. There was nothing that deserved the name before it, yet more than half of the land of the globe has not yet been surveyed, and many geologic problems are yet unsettled, concerning regions that have been studied. The mineralogical relations and precedents among basalts, granites and other rocks, as well as the physical conditions that determined composition, arrangement and distribution, remain to be determined. Volcanic phenomena are not at all well understood. The composition of the interior of the earth is quite unknown; its temperature, and the rate of heat conductivity of the various rocks—questions which, when answered, will have much to say about the age of the earth and especially of the length of time since it has been a habitable body for any living things. At present there are two camps interested in this question, with lower time limits from ten million to a thousand million years. When Asia, Africa and South America have been as well studied as Europe and North America have been, there will probably be found vast stores of metals, coal, oil and valuable minerals, thus adding to the world's stock of needful things. Also the discovery of new varieties of fossils, the ancestors of living species, especially of mankind, missing links, will add to the interest in human affairs. Geologists have for years been trying to find some ​definite measure for geologic epochs, to ascertain how long ago the glacial age was, and how long it lasted. At present there are only surmises that the glacial epoch ended from 10,000 to 50,000 years ago. The twentieth century will probably be able to settle this.
Chemistry too as a science was nineteenth century product. There were guesses and ingenious surmises, but there were no known general laws, such as of definite proportions, of atomic weights, of energy in reactions and the like. It became possible to measure approximately the sizes of molecules and atoms, to know definitely their rates of vibration, and molecular structure is, for many compounds, made out about as well as if they could be dissected and their atoms handled like so many parts of an engine or dynamo.
As knowledge grew on the basis of experiment, generalization of course was attempted, and as physical phenomena were inextricably interwoven with the chemical, constant modifications were required. Not a few propositions found their way into books and general use which had to be abandoned. Thus, it was assumed that when molecules of salt, NaCl, were dissolved in water, each molecule retained its identity and moved as a whole in the liquid. We now know this is not true, but each atom becomes practically independent and moves like a gaseous particle in the air, producing pressure in the same way and for the same reason. The new knowledge has made it needful to revise again some of the notions that were held, and so profound is the change required that some years will be needful to bring chemistry as a science into satisfactory relations with physics. That is not all. We have all been taught and have probably had no misgivings in saying that matter is indestructible. Much philosophy is founded on that proposition. But we are now confronted with the well vouched for phenomenon from two independent workers that under certain conditions a certain mass of matter loses weight, not by mechanical removal of some of its molecules, but by the physical changes which take place in it. This is a piece of news that is almost enough to paralyze a scientifically minded man, for stability of atoms, unchanging quantity and quality, seems to be at the basis of logical thinking on almost all matters. In the 'Arabian Nights' one may expect that the unexpected will happen—genii may be summoned to do this or that, matter may be created or annihilated at will—and the conception gives one pleasure though one knows it to be impossible, and one thinks it impossible because one has never known such changes in matter, and because one has been taught that matter is indestructible. The amount of change is slight in the experiments related, yet well within the possibility of measuring, and one may be sure that from now on the most expert and careful and patient experimenters will attack this question and verify or disprove it. If it be disproved, we shall be philosophically where we have so long been. If it be proved, ​it will be the most stunning fact that has come into science for a hundred years. The nebula theory, the doctrine of evolution, and the antiquity of man will be trifles compared with its significance.
Chemistry, though, with or without that fact, has a wonderful field where one may work intelligently in a constructive way. Compounds both inorganic and organic have been produced in great variety, and some chemists are at work trying to make artificially many things which one has to depend upon nature for now—thus quinine, now used in such great quantity; others are sugar or albumen for food, or nitrates for fertilizers, and so on. All these products, if produced on a commercial scale, would be of enormous worth to the world. Aside from these the chemical preparation of antitoxins for the relief and cure of many diseases, cholera, plague, yellow-fever, typhoid fever, are all being sought for with a great probability that they will be discovered and the life of men be saved for many years. I wish I could say that if life be saved and kept by such artificial means that mankind would not seek other ways of decimating its ranks. The average life of the Jews is upwards of seventy years. If all men had the same degree of vitality the world would be so crowded in a hundred or two hundred years that only the loss of fertility would save the necessity for famine, war and pestilence. Chemistry may give us a boon and leave nature to find some other resource for reducing numbers. That such resource would be radically different from her past methods is not very probable.
Physics is that science which is concerned with transformable energy and its transformations under all kinds of conditions. The energy may be mechanical, chemical, thermal, electrical, gravitational, physiological or mental. So long as they are transformable they are all departments of physics. The nineteenth century correlated them all and showed the conditions for transformation and the nature of several forms, thus heat, as vibratory atomic and molecular motion, radiant energy a wave motion in the ether. The discovery of the ether and many of its phenomena belongs also to it. The development of many arts and industries followed the new knowledge, so we have now, for instance, the electrical industries in many ways, the spectroscope and its astronomical revelations, the telescope grown from a four inch objective to a four foot objective.
The old ideas of the nature of matter or of atoms have all been abandoned and we have come to the conclusion that matter is not inert but is loaded with energy, that indeed the ether is saturated with it, though it is available to us only through the agency of matter, which acts as a transformer and a distributor of it. Yet we need to know much more of it. There is more to be learned about chemistry in its relation to physics than any seems to have considered hitherto. It is the form of energy which is present in atoms. Thus when hydrogen ​and oxygen unite they-give out a surprising amount of energy in the form of heat. A single pound of this combination, taken at ordinary temperature, will give out an amount of heat equal to seven million foot pounds of work, or sufficient to raise a ton one half mile high. We know that heat is a vibratory kind of atomic and molecular motion and the rate of this vibratory motion is the measure of the temperature. The question is as to the antecedent of the heat which thus appears. In what form does energy exist in atoms? Up to this time we have been able to trace energy through its various forms until we come to atoms; there it has eluded us. We say 'chemical energy,' but we have no idea how it differs from heat or from gravitative energy. It is a mystery. What form of motion or stress can be thus embodied? In some way it is related to the ether. It seems as if in some unique manner atoms drew from the ether as from a common reservoir, each particular atom capable of holding so much of that kind and no more, like pint cups and quart cups, and this at once transformed into heat at the instant of combination. When combinations of atoms such as water are decomposed, they again absorb the energy spent to separate them, and an atom therefore possesses more available energy than any combination of atoms. It seems as if atoms acted as transformers of ether energy into the ordinary and familiar forms, such as heat and electricity, and vice versa, transforming the latter into ether energy. When we learn this secret we may likely enough be able to artificially extract from the ether as much energy as we need for any purpose, for as I have said, it is inexhaustible, and every cubic inch of space has enough for all the needs of a man for many days. This seems fairly probable, and when the source of atomic energy is discovered, it will rank with the greatest scientific achievements of all time. We shall know more of the ether, of the structure of matter, of the antecedents of most of the energy we are familiar with, as this phenomenon underlies most if not all of the phenomena in all the sciences.
It is yet regarded as a mechanical paradox that a medium without friction should have waves set up in it by molecular vibration, and little is known of the physical relations existing between matter and ether, by which electrical and magnetic phenomena are produced, and one may say that of the nature of ether we know nothing. Think of the amazing extent of it. As limitless as space itself, with no break or separation of its parts, not made up of particles like matter, but completely filling space and so constituted that any movement of a particle of matter in some way affects the whole body of it to the remotest part of the visible universe.
The nature of gravitation is as unknown as the nature of life itself. We know how it acts, and that this action is millions of times ​quicker than light, but that is all, and the one who unravels the mystery will deserve to rank with the greatest of discoverers.
In like degree are we ignorant of electrical and magnetic phenomena which depend upon the ether. When the ether is understood we shall be able to understand in a mechanical sense how moving a magnet disturbs every other magnet wherever it may be, why chemical compounds are possible, why crystals assume geometric forms, and why cellular structure in plants and animals can embody what we call life. To discover the nature and mode of operation of this ether is the work of the twentieth century, and we may be sure that he who accomplishes this will deserve to rank with the highest; indeed it may fairly be said that in importance it is not secondary to anything known, for it is apparently concerned in all phenomena from atoms to masses as big as the sun.
The biologists have great problems on hand for solution. The nineteenth century work made it clear that all the forms of vegetable and animal life of to-day are the product of slow changes in form and functions of living things reaching back millions of years. The successions of some forms were well worked out and the principle established. We call it evolution and everybody nearly believes that this represents the truth in the matter, but how these changes occur and what necessitates them remain as mysterious as ever. Darwin spoke of natural selection. There were all sorts of variations in progeny, and the ones best fitted to the environments survived, but he gave no reason why there should be variations, and this is the great question to-day. Many are at work to discover this, and some who have worked in this line have stumbled upon some very unsuspected facts. There has been assumed that like would produce like, and that heredity could and would account for abnormal structures when parents for any reason through new environment had acquired new habits or new structures of any kind. Now it has been shown that such changes of structure or of habit seldom if ever appear in the progeny. For instance, no matter how many generations of mice have their tails cut off each new mouse has the same old length of tail. Each lamb has as many tail vertebrae as did those of hundreds of years ago, though all lambs have their tails cut off when young. Such acquired character is not inherited. Nature pays no attention to any changes save such as she herself initiates, and the conditions she herself adopts remain to be found out. Sometimes she makes monsters and sometimes geniuses, but never by external environment, always de novo. This throws overboard the principle good and thoughtful men have so long cherished, that the good habits of one generation would be a hereditary possession of the next. The conditions for heredity are now a most absorbing study among some of the foremost biologists. It is suggestive that at this late day such a reversal of opinion on this ​question has come about and that the question has been rim down to cellular structure and molecular arrangement. It will hardly be gainsaid that a knowledge of the proper conditions for changing forms, functions, habits and motives of living beings will be of priceless value to the race, and this work comes to the twentieth century.
Another piece of work, bringing great surprise among biologists as well as the rest of the thinking world, has been given to us within a year or two, namely, that unfertilized eggs have been made to develop in a normal way by subjecting them to certain inorganic chemical substances, such as magnesium chloride. It has been repeated by so many there is no doubt about it now, but its significance is that life itself is a chemical process and does not necessarily depend upon antecedent life any further than such structure contains chemical combinations of proper sort, and that if these be provided in other ways life and growth will result. This research has no more than begun and we may be on the lookout for surprises. A French biologist reports that if an egg be properly cut into as many as sixteen pieces it will develop into sixteen individuals, differing only in size from the normal individual. This opens out a new field, the philosophical importance of which exceeds its biological importance, as can be seen in a minute's thinking. What the outcome will be no one can tell now, but we may envy the biologists who devote their time to such investigations.
A few years ago two German scientific men discovered that a minute drop of a mixture of oil and a salt of potash acted like a microscopic living thing in several ways. It would move about spontaneously, change its form, had a circulation in itself, would gather to itself particles of other matter in its neighborhood, and was sensitive to stimulus from the outside. It comported itself like a thing of life in all ways but one, it could not reproduce its like. The material itself was called artificial protoplasm. The work is still being investigated, both abroad and at home, with the hypothesis that if the proper chemical constituents can be found and added it will then be a real artificial living thing. As it already possesses four of the five distinguishing characteristics of a living thing, ingenuity and persistence will enable some one to find and endow it with the fifth. It will not be safe for one to predict that this can not be done, for it may be done to-morrow, and the twentieth century starts with a pretty problem considered as a physico-chemical problem but the one who solves it, if it should be done, will have reason to be thankful he is not living in any preceding century, for his life would be made a burden to him, if he was not made a martyr.
I have been told by many good people that this question or that question was quite outside of the domain of science and presumptuous in one to inquire into. Astronomy and geology and chemistry are graciously permitted to be in the hands of the man of science, but life ​and mind phenomena are declared to be outside the province of physical science, yet the same was said about astronomy and geology and chemistry not many generations ago. "Was not Newton condemned for dethroning the Almighty by proposing the law of gravitation for keeping the planets in their orbits? Was not war made upon those who undertook to show that the earth was more than 6,000 years old, and were not the chemists who showed how organic compounds could be formed believed to be enemies of the truth and bent on misleading mankind? Isn't it curious to contemplate that those who know least about a given science should be the ones to set its limits, who know what can not be done or hoped for so much better than those who devote their lives and their best endeavors to discover what is true and what seems probable? To-day men's lives are not endangered as they used to be for their attempts to find an answer to puzzling questions, so the work goes on, and the things discovered are never like what was anticipated by the good and conservative people who know beforehand what can and what can not be known, and it is a bit sad that the latter must die that a new generation may arise to possess the new truth. It took more than two generations to convince the world of the truth of the nebular theory, that the earth was millions of years old, that mankind had occupied the earth for hundreds of thousands of years, and the doctrine of evolution is hardly forty years old, yet are there not many who give it no credence? Perhaps one of the good things which the twentieth century will be able to accomplish will be effectually to warn everybody of the danger of setting any limits to knowledge, also that any opinion mankind has held that has not been through the crucible of science is probably wrong, but the only reason for holding this is that so far every one so tested has been found to be erroneous.
The study of nerves, their connections and activities, has been begun in earnest only within the past few years, but what has been learned seems to lead to as many surprises as has any other branch of science. Only here and there is there now an investigator in this branch, but these have already found out that all nervous action is spent upon the muscles. That all are in one way or another connected with them, that each particular nerve cell has a specific function and substitution seems no more possible among them than can the eye be substituted for hearing or for tasting. At present work is being carried on to determine the functions of various parts of the brain, especially for the effects of use and. disuse, the nature of exhaustion, the rate of recuperation, the source of energy and of automatic activity, what happens in sleep, in the hypnotic state, in disease, insanity and in unconsciousness. Dr. Hall has said that the nerves are the most wonderful things in the world, and we know so little about them. Mind and thinking, conditioned by their presence ​and activity, on the one hand, and all expressions of them through muscular action as exhibited by motions and emotions.
There are many reasons for expecting most important disclosures from this direction, which may make needful many changes in common beliefs in educational theories and efforts, of responsibility in crime and the proper management of defectives of all sorts. It is not unlikely as great changes as took place during the last century in the beliefs on many important subjects will be required for the work of the twentieth century.
So far I have been speaking of science as related knowledge. Knowledge of such a kind as to react upon our opinions of men, of institutions, society, and the universe as a whole, but science is more popularly conceived as improved ways of doing things, of new products and new possibilities in life, of the arts as managed for economy of effort, enhancing comfort and removing the stress of living. These, however, are not science, but the products of science, and every one is properly concerned to know what changes are likely to come from such a source. The mechanic arts of the last century worked a wonderful change in the modes of living, in the variety and kinds of wants. If we could be deprived suddenly of all save such things as could be had a hundred years ago, we should all be made as miserable as one can think, yet those who lived a hundred years ago were no more miserable than we are. They got as much out of their lives as we do out of ours, and never suffered from thinking they did not have railways, telegraphs, telephones, steamships, automobiles and weather forecasts. These things could never be missed as no one had ever had them, and perhaps most people would have thought a prophet of them to be a romancer.
Many lessons have been drawn from history with the expectation that we may the better order our lives. How many historians there have been, and how few are those whose interpretations have not been wrong! One may recall that squib by Bishop Stubbs, of Oxford, whose, contempt for Froude was profound. Canon Kingsley had resigned the chair of history at the university, assigning as reason that what had been understood to be history was unfounded.
While Froude instructs the Scottish youth That parsons never tell the truth, The Reverend Canon Kingsley cries That history is a pack of lies.
These strange results who shall combine? One plain reflection solves the mystery, That Froude thinks Kingsley a divine While Kingsley goes to Froude for history.
One might once fairly have inferred that leisure was what all ​mankind desired. The invention of labor-saving devices, so-called, the cotton gin, the factory loom, the sewing machine et al. has turned out sociologically to be very different from that, for the time saved from the old methods has been fully occupied in doing more work, raising more cotton, weaving more cloth, making more clothes. Men have not more leisure because they want something else more than they want leisure. Tastier food and personal adornment are the things that bring the chief stress upon life.
Leisure and idleness are not identical. Leisure is the relief from the stress for maintaining life. There is no leisure for one whose whole time is required to supply food, clothing and shelter for himself and others. When these demands can be met in less than the whole time, the remainder may be called his leisure time and this may be spent in idleness, that is, doing nothing, or it may be spent in doing something else in accordance with one's tastes, aptitudes and opportunities. One may read or study or write or travel, or one may add to one's income by working overtime or at other occupations. Such an one has leisure which he employs in ways that give him a measure of satisfaction. What is called a higher standard of living is almost always the immediate result of leisure—more palatable food, better clothes and houses. If one spends all his income to provide himself with better things than are really needful to keep him healthy, he can not say he has no leisure, for there is no limit to what may be called better things which one may possess and be no healthier or happier. Do not the so-called poor outlive the rich? Whence the centenarians of all countries, Indians, Mexicans, Negroes? Does not nature take as loving care of tramps as she does of the so-called good citizens, who faithfully work and save and build?
To be beyond compulsion to do anything is desirable, of course, for whoever is compelled is so far a slave. During the nineteenth century we were all urged by advice, example and mottoes that thrift was the chief thing. One who did not respond to the pressure was stigmatized as lazy. The hustler was the admired type from pupil to preacher. High speed has been demanded in living as well as on railroads, and he who could not or would not keep up has often had a hard time to live at all. The assumption in all this was that life should be strenuous. Our energetic President has publicly urged this. But there are many reasons for holding that it is all wasteful, loading life with miseries and not at all in accordance with Nature's plan. Nature is never in a hurry. She takes ten thousand years to make Niagara Falls and a hundred thousand years to make man, and she spares neither her own work nor man's, as if neither is worth the keeping. In Babylon of old were there not Morgans and Rockefellers, many storied buildings and great armies? Nature has transformed men and armies into gas and shrubbery, the buildings into tumuli, and made a ​desert of the gardens. How much better to-day is the world for their energy, their strenuousness and their power? Are we any more lovable or stronger or wiser?
I have sometimes amused myself wondering what question I would ask an inhabitant of Mars, if communication with that planet could be established. If but one question could be answered, what should that question be? Is there any one question which everybody would be willing to have asked and forego every other one? Would it be a question of astronomy or of biology or of philosophy? Each one should settle for himself what that question ought to be, if its answer was to be of interest to all mankind. If it were of a religious or philosophical kind, think what happiness or misery would befall the most of us when the answer came. It would be almost like a judgment day and half the world or more would be thrown into a suicide mood. Ignoring momentous questions, what others are we really most concerned to have answered? Do we not all want to know of the nature of life, of mind, and of all the activities of nature displayed in phenomena? Does not everybody ask, 'What is electricity?' 'What is life?' I do not remember ever to have heard the question 'What is gravitation?' though it is certainly one of the most obscure of all the great activities of nature. Not a particle of matter escapes its hold, and the law of inverse squares we have all learned so glibly, we take on the basis of uniform experience. How can such action be the outcome of inherent properties of matter, and what must be the texture and distribution in the ether so compelling?
Surmises by the score have been made, but none are satisfied with any attempt to find a reason or the antecedents of the phenomenon. It conditions every phenomenon of every kind that comes to our knowledge in a gravitative way, but hitherto it has quite eluded the most ingenious of guessers, and most persons who have been concerned with its problems have either abandoned attempts at its solution or have unwarrantably concluded it is insoluble. There is no good reason why it should be thought of as an ultimate problem, and its solution belongs to the twentieth century or some of its successors. In my judgment its rationale will be found some time.
When, a hundred years ago, men said that heat was caloric, it is plain on a little thinking that such an answer brought us no nearer the real solution. Giving the thing a new name was not an explanation. We have been taught for a generation that heat is a mode of motion, and when we now think of the phenomena we think of brisk changes of position of the minute particles of a body, and that idea reveals heat as a condition of matter, not a thing in itself any more than the spin of a top is to be thought of as a thing to be described apart from the top.
A hundred years ago light was thought to be a kind of corpuscle ​and now we call it a wave motion in the ether, and say there is no such thing as light, it is merely a condition of the ether in the same sense as heat is a condition of matter; and there are some physicists who go farther and declare it to be only an optical illusion, a physiological phenomenon and does not exist apart from the mechanism of the eye. Such have proposed we discard the word light from physical science, seeing it is only a condition of the optical apparatus. At any rate, the nature of light is now so well known and understood that no one thinks of asking the question 'What is light,' hut the answer we give is a long remove from the answer expected a hundred years ago.
Here on the threshold of the new century we are confronted with the question 'What is electricity?' and the answer implied by the question seems to demand a something which could be described by one who knew enough, as one would describe some new mineral or gas or thing. Some eminent scientific men are befogged by the question, say it is some ultimate unknowable thing, and hopeless as an inquiry. If it be a something it must be described by its constant properties as other things are. If it be unlike everything else then it can not be described by terms that apply to anything else. All material things have some common properties. A glowing coal is an incandescent solid, a flame is an incandescent gas, but neither glow nor flame exists apart from the matter that exhibits the phenomena. Both are conditions of particular kinds of matter.
If electric phenomena are different from gravitative or thermal or luminous phenomena it does not follow that electricity is miraculous or that it is a substance. We know pretty thoroughly what to expect from it, for it is as quantitatively related to mechanical and thermal and luminous phenomena as they are to each other; so if they are conditions of matter, the presumption would be strongly in favor of electricity being a condition or property of matter, and the question 'What is electricity?' would then be answered in a way by saying so, but such an answer would not be the answer apparently expected to the question. To say it was a property of matter would be not much more intelligible than to say the same of gravitation. At best it would add another property to the list of properties we already credit it with, as elasticity, attraction and so on. In any case the nature of electricity remains to be discovered and stated in terms common to other forms of phenomena, and it is to be hoped that long before this new century shall have been completed, mankind will be able to form as adequate an idea of electricity as it now has of heat.
What thoughtful person has not asked 'What is life?' Many and long answers have been given to this question. One has said 'Electricity is life.' Another 'Life is the continuous adjustment of the internal relations to the external relations.' Which definition tells rather what life does than what it is. Some have imagined it to be ​a kind of force, called vital force which presides over the phenomena of living things which may be now in and now out of the matter of the living thing. Vital force as such was mostly discarded as a physiological factor a good many years ago, and in its place was put physical and chemical forces, and to-day most physiologists say that life is reducible to physical and chemical agencies; if it be true, it is not much of an answer to the question 'What is life?' for it leaves us still the question to be intelligibly answered as is the question as to the nature of heat. If one recalls how it has fared with the other queries where more knowledge has given a new and unexpected answer to each, one would be led to anticipate an answer quite different from the one somehow imagined. However it may turn out, there is evidently much work to be done and the twentieth century has the problem plainly before it.
Once more the relation of mind to body waits an answer. Is mind to be thought of as a somewhat, resident in a body, but not necessarily a part of it? If one calls it soul or spirit and thinks of it as separated from body, yet with the same attributes, capable of being now here and now there by an act of volition, unrestrained by physical factors as gravity or heat or the rest, he evidently gets the idea from his philosophy of things in which he assumes limits to the properties of matter before he has exhausted its possibilities and functions. It can not be denied that the physiological psychologists have lately been finding mind all through the bodily structure and giving an entirely different conception of soul from that usually held. However it be in reality, the problem is clearly before the twentieth century workers, and one must rest in agnosticism about it until the knowledge comes.
It seems clear that we have much to learn as to the nature of all the forms of energy, and one appears to be as mysterious as any other, though some of them, like gravitation, are so common and so constant that they awaken no curiosity in most persons and seem to be quite unrelated to personality or to philosophical and religious matters. It seems probable that whoever shall find the meaning of any of these factors will have at hand means for the disentanglement of the whole. With all these problems to be solved is there not enough for the work of the century? and whoever shall catalogue the triumphs of the twentieth century, if he can point to all these or a good part of them will have reason for holding that this century has accomplished as much and as important work as did its predecessor, the nineteenth.