Progress of Scientific Discovery in the Past
Science by no means belongs to the nineteenth century. It has been extant upon the earth ever since man began to observe and consider the marvels of the universe. We can trace it back to an age possibly ten thousand years remote, when men began to watch and record the movements of the stars in the heavens above the broad Babylonian plain. It grew active among the Greeks of Alexandria in that too brief period before the hand of war checked for centuries the progress of mankind. It rose again in Europe during the mediæval period, and became active during the later centuries of this period. In the centuries immediately preceding the nineteenth numbers of great scientists arose, and many highly important discoveries were made, while theoretical science achieved a remarkable progress, its ranks being adorned by such names as those of Copernicus, Kepler, Galileo, Newton, and various others of world-wide fame that might be given. Thus at the dawn of the nineteenth century there existed a great groundwork of scientific facts and theories upon which to build the massive future edifice.
Scientific Activity of the Nineteenth Century
This building has been going on with extraordinary rapidity during the present century, and to-day our knowledge of the facts of science is immensely greater than that of our predecessors of a century ago; while of the views entertained and theories promulgated previous to 1800, the great sum have been thrown overboard and replaced by others founded upon a much wider and deeper knowledge of facts.
New and important theoretical views of science have been reached in all departments. Recent chemistry, for instance, is a very different thing from the chemistry of a century ago. Geology has been largely transformed within the century. Heat, once supposed to be a substance, is now known to be a motion; light, formerly thought to be a direct motion of particles, is now believed to be a wave motion; new and important conceptions have been reached concerning electricity and magnetism; and our knowledge of the various sciences that have to do with the world of life is extraordinarily advanced. As for the practical applications of science, itmay suffice to present the startling fact that the substance of the atmosphere, scarcely known a century ago, can now be reduced to a liquid and carried about like water in a bucket.
In view of the facts here briefly stated it might almost be said that science, as it exists to-day, is a result of nineteenth century thought and observation; since that of the past was largely theoretical and the bulk of its theories have been set aside, while the scientific observations of former times were but a drop in the bucket as compared with the vast multitude of those of the past hundred years. As regards the utilization of scientific facts, their application to the benefit of mankind, this is almost solely the work of the century under review, and in no direction has invention produced more wonderful and useful results.
Wallace’s “Wonderful Century”
Epoch-Making Discoveries of Past Times
Alfred Russell Wallace, one of the most distinguished scientists of recent times, in his work entitled “The Wonderful Century,” has made a careful inventory of the discoveries and inventions to which the progress of mankind is mainly due, and he divides them into two groups, the first embracing all the epoch-making discoveries achieved by men previous to the present century, and the second taking in the steps of progress of equal importance which have been made in the nineteenth century. In the first list he finds only fifteen items of the highest rank, and the claims of some even of these to a separate place are not beyond question, since they may not really be of epoch-making character. He puts first in the list the following, viz.: Alphabetic writing and the Arabic notation, which have always been powerful engines of knowledge and discovery. Their inventors are unknown, lost in the dim twilight of prehistoric times. As the third great discovery of ancient times he names the development of geometry. Coming after a vast interval to the fourteenth century A. D., we find the mariner’s compass, and in the fifteenth the printing press, both of which beyond question are of the same character and rank as alphabetic writing.Epoch-Making Discoveries of Past TimesFrom the sixteenth century we get no physical invention or discovery of leading importance, but it witnessed an amazing movement of the human mind, which in good time gave rise to the great catalogue of advances of the seventeenth century. To this he credits the invention of the telescope, and, though not of equal rank, the barometer and thermometer (which he classes as one discovery), and in other fields the discovery of the differential calculus, of gravitation, of the laws of planetary motion, of the circulation of the blood, and the measurement of the velocity of light. To the eighteenth century he refers the more important of the earlier steps in the evolution of the steam engine and the foundation of both modern chemistryand electrical science. This completes the list. To the above many would add Jenner’s discovery of vaccination and probably several others. Each writer, in making up such a list, would be governed in a measure by his personal range of studies, but no one would be likely to deviate widely from the above list.
Great Discoveries of the Nineteenth Century
Now what has been the record since 1800? How does the nineteenth century compare with its predecessors? In Wallace’s view it is not to be compared, as regards scientific progress and discovery, with any single century, but with all past time. In fact, it far outstrips the entire progress of mankind in the ages preceding 1800.
Estimating on the same basis as that which he previously adopted, Wallace finds twenty-four discoveries and inventions of the first class that have had their origin in the nineteenth century, against the fifteen enumerated from all previous time.
Of the same rank with Newton’s theory of gravitation, which comes from the seventeenth century, stands out the doctrine of the correlation and conservation of forces, one of the widest and most far reaching generalizations that the mind of man has yet reached. Against Kepler’s laws of planetary motions from the seventeenth century we can set the nebular theory of the nineteenth. The telescope of the seventeenth is matched by the spectroscope of the nineteenth. If the first reveals to us myriads of suns, otherwise unseen, scattered through the illimitable fields of space, the second tells us what substances compose these suns and maintain their distant fires, and, most wonderful of all, the direction and the rate in which each is moving. Harvey’s immortal discovery of the seventeenth century finds a full equivalent in the germ theory of disease of the nineteenth. The mariner’s compass of the fourteenth century easily yields first place to the electric telegraph of the nineteenth, while the barometer and thermometer of the seventeenth century are certainly less wonderful, though perhaps not less serviceable, than the telephone and phonograph and the Röntgen rays of our own day.
Useful and Scientific Steps of Progress
We may more briefly enumerate the remaining discoveries cited by Wallace, partly, as will be perceived, mechanical, but mainly results of scientific research. Early in the century came the inestimable inventions of the railway engine and the steamboat, and somewhat later the minor but highly useful discoveries of the lucifer match and of gas illumination. These were quickly followed by the wonderful discovery of photography, than which few things have added more to the enjoyment of man. Equally important in relationto his relief from suffering are the remarkable discoveries of anæsthetics and the antiseptic method in surgery. Another of the great discoveries of the age is that of the electric light, with its remarkably rapid development and utilization.
More purely scientific in character are Mendeljeff’s discovery of the periodic law in chemistry, the molecular theory of matter, the direct measurement of the velocity of light, and the remarkable utility of floating dust in meteorology. The list concludes with the geological theory of the glacial age, the discovery of the great antiquity of man, the cell theory and the doctrines of embryological development, and last, but, in pure science, perhaps the greatest, Darwin’s famous theory of organic evolution—developed by Spencer into universal evolution.
It is quite possible that other nineteenth century scientists would be tempted to expand this list, and perhaps add considerably to Wallace’s twenty-four epoch-making discoveries. Indeed, since his book was written, a twenty-fifth has arisen, in the discovery of wireless telegraphy, the scientific marvel of the end of the century, too young as yet for its vast possibilities to be perceived. We might also mention the electric motor and liquid air as of equal importance with some of those enumerated.
Foster’s Views on Recent Progress
An interesting review of the advances made in science during the nineteenth century was offered by Sir Michael Foster, President of the British Association in its 1899 meeting, from which we may quote. He first touched upon chemistry. The ancients, he said, thought that but four elements existed—fire, air, earth, and water. Anything like a correct notion of the composition of matter dates from the latter part of the eighteenth century, when Priestley and Lavoisier revealed to the world the nature of oxygen, and thus led to a long series of fruitful discoveries.
The whole history of electricity as a servant of man is confined to the last sixty or seventy years, and really springs from Volta’s invention of the galvanic battery. Frictional electricity had long been known, but nothing beyond curious laboratory experiments were conducted with it. The investigations and discoveries of Oersted and Faraday, which made possible the telegraph, dynamo, trolley car and telephone, followed Volta’s discovery of the means of producing a steady current of electricity—first announced in 1799.
Geology, too, he states to be a new born science. Although numerous ingenious theories were entertained in regard to the origin and significance of the strata rock, it was only at the close of the eighteenth century that men began to recognize that the earth’s crust, with its various layers of rock, wasa vast book of history, each leaf of which told of periods of thousands or millions of years. The slow processes of formation, and the embedding of the remains of the animal and vegetable life of those ancient times, were only interpreted aright after Hutton, Playfair and Cuvier had wrestled with the problem.
Headlights of Progress
With these interesting views of prominent scientists, we may proceed to a more detailed consideration of the scientific triumphs of the century. To present anything other than the headlights of its progress, in the space at our command, would be impossible, in view of the extraordinary accumulation of facts made by its many thousands of observers, and the multitude of generalizations, of the most varied character, offered by the thinkers in the domain of science. These generalizations vary in importance as much as they do in character. Many of them are evidently temporary only, and must fall before the future progress of discovery; others are founded upon such a multitude of significant facts, and are of such inherent probability, that they seem likely to be as permanent as the theories of Galileo, Kepler, Newton, and others of the older worthies.
Discoveries in Astronomy
Beginning with astronomy, the oldest and noblest of the sciences, we could record a vast number of minor discoveries, but shall confine ourselves to the major ones. Progress in astronomy has kept in close pace with development in instruments. The telescope of the end of the century, for instance, has enormously greater space-penetrating and star-defining powers than that used at the beginning, and has added extraordinarily to our knowledge of the number of stars, the character of their groupings, and the constitution of solar orbs and nebulæ. These results have been greatly added to by the use of the camera in astronomy, the photograph revealing stellar secrets which could never have been learned by the aid of the telescope alone. This has also the great advantage of placing on record the positions of the stars at any fixed moment, and thus rendering comparatively easy the detection of motions among them.
Revelations of the Spectroscope
But it is to a new instrument of research, the spectroscope, that we owe our most interesting knowledge of the stars. This wonderful instrument enables us to analyze the ray of light itself, to study the many lines by which the vari-colored spectrum is crossed and discover to what substances certain groups of lines are due. From studying with this instrument the substances which compose the earth, science has taken to studying the stars, and has found that not only our sun, but suns whose distance is almost beyond the grasp of thought, are made up largely of chemical substances similar to those that exist in the earth.A second result of the use of this instrument has been to prove that there are true nebulæ in the heavens, masses of star dust or vapor not yet gathered into orbs, and that there are dark suns, great invisible orbs, which have cooled until they have ceased to give off light. A third result is the power of tracing the motions of stars which are passing in a direct line to or from the earth. By this means it has been found that many of the double or multiple stars are revolving around each other. A late discovery in this direction, made in 1899, is that the Polar star, which appears single in the most powerful telescope, is really made up of three stars, two of which revolve round each other every four hours, while the two circle round a more distant companion.
New Facts in the Solar System
Late astronomy has revealed to us many marvels of the solar system. Before the nineteenth century it was not known that any planetary bodies existed between Mars and Jupiter. On the first day of the century—January 1, 1801—Ceres, the first of the asteroids or planetoids, was discovered. Three others were soon discovered, and later on smaller ones began to be found in multitudes, so that by the end of the century not less than four hundred and fifty of these small planetary bodies were known. Of other discoveries we may briefly refer to the new facts discovered concerning comets and meteors, planets and satellites, the condition of the sun’s surface, the detailed knowledge of the surface conditions of Mars and the Moon, the character of Saturn’s rings, the discovery of the planet Neptune etc., all due to nineteenth century research.
The Advance of Chemistry
In the group of sciences known under the general title of Physics—chemistry, light, heat, electricity, and magnetism—the progress has been equally decided and many of the discoveries of almost startling significance. Chemistry, as it exists to-day, is almost wholly a child of the century. Many chemical substances were known in the past, but their number sinks into insignificance as compared with those of late discovery. Of chemical conceptions of earlier date, Dalton’s theory of atoms is the only one of importance that still exists. The view long maintained—until late in the nineteenth century, in fact—that organic and inorganic chemistry are separated from each other by a wide gap, is no longer held. Hundreds of organic substances, some of them of great complexity, have been made in the chemist’s laboratory, and can now be classed as properly with inorganic as with organic substances. The gap has been closed, and there is now but one chemistry. Only the most intricate chemical compounds still lie beyond the chemist’s grasp, and the isolation of these may be at any time overthrown. Organic chemistry has become simply the chemistry of carbon-compounds.
BARON F. H. ALEXANDER VON HUMBOLDT.LOUIS AGASSIZ.CHARLES DARWIN.THOMAS H. HUXLEY.ILLUSTRIOUS MEN OF SCIENCE, 19TH CENTURY
BARON F. H. ALEXANDER VON HUMBOLDT.LOUIS AGASSIZ.
BARON F. H. ALEXANDER VON HUMBOLDT.
BARON F. H. ALEXANDER VON HUMBOLDT.
LOUIS AGASSIZ.
LOUIS AGASSIZ.
CHARLES DARWIN.THOMAS H. HUXLEY.
CHARLES DARWIN.
CHARLES DARWIN.
THOMAS H. HUXLEY.
THOMAS H. HUXLEY.
ILLUSTRIOUS MEN OF SCIENCE, 19TH CENTURY
PASTEUR IN HIS LABORATORYThe discovery of the mission of the exceedingly minute organisms known as bacteria in producing disease ranks among the greatest and most beneficient of our age. By it the art of the physician was first raised to the rank of a science. The honor of this discovery belongs to Louis Pasteur, the eminent French chemist and biologist.
PASTEUR IN HIS LABORATORY
The discovery of the mission of the exceedingly minute organisms known as bacteria in producing disease ranks among the greatest and most beneficient of our age. By it the art of the physician was first raised to the rank of a science. The honor of this discovery belongs to Louis Pasteur, the eminent French chemist and biologist.
One chemical theory of recent date, the vortex atom theory of Lord Kelvin, has quickly met its fate, being abandoned by its author himself, but the study of it has been rich in results. It is now widely held that the universe is made up of two great basic elements, ether and matter, or perhaps one only, since it seems highly probable that the atom of matter is a minute, self coherent mass of ether. It is further held as doubtful that atoms ever exist alone, they being combined by their attractions into small bodies known as molecules, which are in incessant motion, and to whose activity the physical force of the universe is largely due.
One of the most important chemical discoveries of the century was that of the “periodic law” of the chemical elements, advanced by the Russian scientist Mendeljeff, under which the weights of the atoms of the elements were for the first time placed in harmony with each other, and a fixed numerical relation shown to exist between them. We may conclude this brief glance at the science by mention of the very high temperature which the electric furnace has now placed at the command of chemists, and the equally great refrigeration now attainable, by which the air itself can easily be liquified and even frozen into a solid mass.
Light and Its Phenomena
Light, naturally one of the earliest of the phenomena of nature to attract the attention of man, was little understood until after the advent of the nineteenth century. It was of old supposed to be a substance of so rapid motion as to be practically instantaneous in its movement through space. Even Newton looked upon it as a substance given off by shining bodies, and it remained for Young, in the beginning of the nineteenth century, to prove that light is not a substance but a motion, a series of rapid waves or undulations in a substance extending throughout space, and known as the lumeniferous ether. The idea that light is instantaneous in its motion also vanished when Roemer discovered, by observing the eclipses of Jupiter’s moons, that it takes about eight minutes for the ray of light to travel from the sun to the earth. A cannon ball moving at the rate of 1,700 feet per second would take about nine years to make the same journey, the wave of light traveling at the extraordinary speed of over 186,000 miles in a second. Yet immensely rapid as is this rate of movement, we do not need to go to the sun and planets to measure the speed of light, but can now do so, by the use of delicate instruments, on a few miles of the earth’s surface. This is one of the great discoveries enumerated by Wallace.
Late Discoveries in Optics
The discoveries in relation to the constitution and characteristics of light made during the century have been so numerous that we must confine ourselves to those of major importance. Much might be said about thephenomena of polarization, refraction, diffraction, photography, and the development of the power of lenses, to which the great advance in telescopic and microscopic observation is due. Among these steps of progress perhaps the most interesting is the development of instantaneous photography, a striking result of which is the power, by aid of photographs taken in rapid succession, of portraying objects in motion—living pictures, as they are called—an exhibit now so common and so marvelous. But among all the advances in the science of optics the most important are spectrum analysis and the Röntgen ray. The remarkable discoveries made in astronomy by the former of these have been already stated. The Röntgen ray, which has the power of rendering ordinarily opaque substances transparent, has become of extraordinary value in surgery, as showing the exact location of foreign substances within the body, the position and character of bone fractures, etc.
Heat as a Mode of Motion
Heat, once looked upon as a substance, and known by the now obsolete name of Caloric, has been demonstrated to be, like light, a motion, the incessant leaping about of the molecules of matter, this motion being readily transferable from one substance to another, and forming the great substratum of power in the universe. This theory, first promulgated by Count Rumford, an American by birth, was fully worked out by others, and put in popular form by Professor Tyndall, an English scientist, in his “Heat Considered as a Mode of Motion,” published in 1862. Radiant heat is identical with light, being a vibration of the ether. It may be further said in relation to heat phenomena that remarkable power in producing very high and extremely low temperatures is now possessed. By the former the most refractory substances may be vaporized. By the latter the most volatile gases may be liquified and even frozen. The point of absolute zero, that in which all heat motion would disappear, is estimated to be at the temperature of 274 degrees 6 minutes centigrade below the freezing point of water. A degree of cold within some forty degrees of this has been reached in the liquefaction of hydrogen. In 1889 the climax in this direction was reached in the reduction, by Professor Dewar, of the very volatile element hydrogen to the solid state.
Conservation and Correlation of Forces
Electricity, formerly, like heat and light, looked upon as a substance, is now known to be a motion, being, in fact, identical in origin with light and radiant heat. All these forces are considered to be motions of the lumeniferous ether, their principal distinction being in length of wave. In fact, it is easy to convert one of them into the other, and the great doctrine of the conservation and correlation of forces means simply that heat, light and electricity may bemutually transformed, and that no loss of motion or force takes place in these changes from one mode of motion to another. In the operation of the electric trolley car, to offer a familiar example, the heat power of coal is first transformed into engine motion, then into electricity, then again into light and heat within the car, then into mass motion in the motor, and finally passes away as electricity. No better example of the “correlation of forces” than this familiar instance could be adduced.
Applications of Electricity
As regards the nature of electricity, though innumerable observations have been made during the nineteenth century and a vast multitude of facts put upon record, we know little more than is above stated. But if we turn to the practical applications of electric power, it is to find these standing high among the great advances of the century. To it we owe the highly important discoveries of the telegraph and the telephone; the conversion of engine power into electricity by the dynamo and the use of this in moving cars, carriages and machinery; the storage battery, with its similar applications; the use of electricity in lighting and heating, the latter remarkably exemplified in the electric furnace, which yields the highest temperature known on the earth; the welding of metals by electricity; the electrotype and electro-plating; the conversion of water power into electric force and its transportation by wire for long distances; the therapeutic uses of the electric current, and other applications too numerous to mention.
The Principles of Magnetism
In regard to the magnet, the handmaid of electric power, we know little other than that the force displayed by it seems to be a result of some mode of rotation in the atoms or molecules of matter, since all the effects of magnetism can be produced by the rotary motion of the electric current in spirals of wire. From this it is thought that the molecular motion to which magnetism is due may be of an electric character, though the permanence of the magnetic force renders this very doubtful. It seems most probable that magnetism is a result of some special condition of the ordinary, inherent motions of atoms—not their fluctuating heat activities, but those fixed motions upon which their organization and persistence depend. The readiness with which soft iron can be magnetized and demagnetized by the use of the electric current is of extraordinary value in the practical applications of electricity. To this fact we owe the dynamo and the electric motor, with all their varied uses.
With this passing glance at the physical forces, we may proceed to the consideration of the great science of geology, which, as above stated by Foster, is a new-born science, almost wholly of nineteenth century development. Geology as it now exists may be said to date from 1790, whenWilliam Smith published his “Tabular View,” in which he showed the proper succession of the rock strata and pointed out that each group of rocks is marked by fossils peculiar to itself. With his work began that great series of close observations which still continue, and which have laid the constitution of the earth’s crust open before us in many of its intimate details.
Progress in Geology
Among the many geologists of the century Sir Charles Lyell stands prominent, his “Principles of Geology” (1830–33) forming an epoch in the advance of the science. Before his time the seeming breaks in the series of the rocks were looked upon as the results of mighty catastrophes, vast upheavals or depressions in the surface, which worked widespread destruction among animals and plants, these cataclysms being followed by new creations in the world of life. Lyell contended that the forces now at work are of the same type as those which have been always at work; that catastrophes have always been local, as they are now local; that general forces have acted slowly, and that there has been no world-wide break, either in rock deposits or the progress of human beings.
His views gave rise to a conception of the unbroken continuity of organic life which was greatly strengthened by the publication of Charles Darwin’s “Origin of Species,” which went far to do away with the old belief that each new life-form has arisen through special creation, and to replace it by the theory now widely held that all new forms of life arise through hereditary descent, with variation, from older forms. In this conception we have the basis of the recent theory of evolution, so thoroughly worked out and widely extended since Darwin’s time—a theory including the doctrine that man himself is a result of descent, and not of special creation.
The Nebular and Meteoric Hypotheses
With geology is closely connected the Nebular Hypothesis of Kant and Laplace, of eighteenth century origin, to the effect that all the spheres of space originated in the condensation and rotation of immense volumes of nebulous vapor, similar to the nebulæ now known to exist in the heavens, and that each planet began its existence as a great gaseous globe, its evolution being due to the gradual process of cooling and condensing, by which its surface, and perhaps its whole mass, were in time converted into solid matter. This interesting doctrine of world evolution does not remain unquestioned. A new hypothesis was advanced by Professor Lockyer in the final decade of the nineteenth century, to the effect that spheral evolution is not due to the condensation of gaseous nebulæ, but of vast aggregations of those meteoric stones with which space seems filled, and which are drawn together by their mutual attractions, become intensely heated through their collisions, and areconverted into liquids and gases through the heat thus evolved. It is possible that the visible nebulæ, like the comets, are great volumes of such meteors. This is the meteoric theory referred to in Wallace’s category of great discoveries. It is still, however, far from being established.
The Science of Meteorology
Meteorology, the study of the atmosphere and its phenomena, is another science to which much attention was given during the century under review. A vast number of facts have been learned concerning the atmosphere, its alternations of heat and cold, of calm and storm, of pressure, of diminution of density and loss of heat in ascending, and of its fluctuations in humidity, with the variations of sunshine and cloud, fog, rain, snow, hail, lightning and other manifestations.
The study of the winds has been a prominent feature in the progress of this science, and our knowledge of the causes and character of storms has been greatly developed. The theory that storms are due to great rotary movements in the atmosphere, immense cyclonic whirls, frequently followed by reverse, or anti-cyclonic, movements, has gone far to clear up the mystery of the winds, while the destructive tornado, the terrific local whirl in the winds, has been closely studied, though not yet fully understood. These close observations of atmospheric changes have given rise to the Weather Bureau, by which the kind of weather to be looked for is predicted for the United States. Similar observations and predictions have been widely extended among civilized nations. This is a practical application in meteorology which has been of immense advantage, particularly in the field of navigation.
Progress in the Biological Sciences
Of the sciences with which the nineteenth century has had much to do, those relating to organic life, classed under the general title of biology, stand prominent, which includes botany and zoology. Subsidiary to these are the sciences of anatomy, physiology, embryology, psychology, anthropology, and several others of minor importance. We have, here laid out before us a very large subject, which has made remarkable progress during the past hundred years, much too great to handle except in brief general terms.
In botany and zoology alike, the development of the cell theory is one of the most conspicuous advances of the century. It has been shown clearly that all plants and animals are made up of minute cells, semi-fluid in consistency, and principally made up of a highly organized chemical compound known as protoplasm, which Huxley has denominated the “physical basis of life.” These cells are the laboratories of the system. Motions and changes take place within them. They increase in size and divide in a peculiarmanner, thus growing in number. Many of them have self-motion like that of the low forms known as amœbæ. Various chemical substances are elaborated in them, such as the osseous structure of animals, the wood-fibre of plants, and others which are given off into the sap or the blood. In short, they are the foundation stones of life, and the physical operations of the highest beings are made up of the combined and harmonized activities of these myriads of minute cells.
Classification of Plants and Animals
It would be impossible, unless we should devote a volume to the subject, to do justice to the progress of botany and zoology in the nineteenth century. This progress consists largely in observation and description of a vast multitude of varied forms, with the consequent study of their affinities, and their classification into family groups, ranging from species and varieties to orders and classes, or from minor and local to major and general groups. Both plants and animals have been divided up into a number of great orders, ranging in the former instance from the microscopic bacteria to the great and highly organized exogens, and in the latter from the minute unicellular forms to the mammalia. We have here, aside from the cell-theory, and the great progress in classification, nothing of epoch-making significance to offer, and are obliged to dismiss these subjects with this brief retrospect.
Division of the Cell
There are, however, two fields in which an important accumulation of facts in reference to organic life has been made, those of embryology and palæontology. The study of the organic cell by the microscope is one of the basic facts of embryology, since living operations take place within this cell. The network of minute fibres, of which it is largely made up, is seen to gather into two star-shaped forms with a connecting spindle of fibres, the division of which in the centre is followed by the division of the cell into two. This is the primary fact in reproduction, new cells being thus born. In higher production two cells, arising from opposite sexes, combine, and their growth and division give rise to the organs and tissues of a new living being. It is the development of these organs and tissues that constitutes the science of embryology.
The Sciences of the Embryo and the Fossil
The observation, under the microscope, of the stages of this development, has been of the highest value in the study of animal origin, and has aided greatly in the classification of animals. Many old ideas died out when it was clearly shown that all life begins in a single cell, from which the organs of the new being gradually arise. The most important lesson taught by embryology is that the embryo in its development passes through various stages of its ancestry, resembling now one, now another, of the lower animals, and gains for a brief time organs which some of its ancestorspossessed permanently. Of these facts the most significant is that the embryo of man develops gill-slits like those which the fish uses in breathing. These are of no use to it and soon disappear, but their appearance is very strong evidence that the fish form lay in the line of man’s ancestry, and that man has developed through a long series of the lower animals.
In palæontology, or the study of fossil forms of animals and plant life, we have the embryology of races as contrasted with that of individuals. The study of the multitude of these forms which has been collected within the past century has enabled man to fill many of the gaps which formerly appeared to divide animal forms, and has furnished very strong arguments in favor of the descent of new species from older ones. One of the most striking of these facts is that in relation to the horse, of which a practically complete series of ancestral forms have been found, leading from a small five-toed animal, far back in geological time, through forms in which the toes decrease in number and the animal increases in size until the large single-toed horse is reached.
Two other organic sciences, those of anatomy and physiology, have added enormously to our knowledge of animated nature. Anatomy, which is of high practical importance from its relation to surgery, is a science of ancient origin, many important facts concerning it having been discovered by the physicians of old Greece and Rome. This study continued during later centuries, and by the opening of the nineteenth the gross anatomy of the human frame was fairly well known, and many facts in its finer anatomy had been traced. In later anatomical work the microscope has played an active part, and has yielded numbers of important revelations.
Comparative Anatomy
What is known as comparative anatomy has formed perhaps the most important field of nineteenth century study in this domain of science. Though this branch of anatomical study is as old as Aristotle, little was done in it from his time to that of Cuvier, who was the founder of the science of palæontology, and the first to show that the forms and affinities of fossil forms could be deduced from the study of existing animals. If a fossil jaw were found, for instance, with the teeth of a ruminant, it could be taken for granted that it came from an animal whose feet had hoofs instead of claws. It is often said that Cuvier could construct an animal from a single bone, and though this is saying much more than the facts bear out, he did make some marvelous predictions of this kind.
Predictions Concerning Fossil Animals
A notable triumph of the science of comparative anatomy was the prediction made by Cope, Marsh, and Kowalewsky, from the fact that specializedforms are preceded by others of more generalized structure, that an animal must once have existed with affinities, on the one hand, with hoofed animals, and on the other with the carnivores and the lemurs. This prediction was fulfilled in the discovery of the fossil Phenacodus in the Eocene deposits of the western United States. The study of comparative anatomy, particularly in its application to fossil forms, has aided greatly in the acceptance of the doctrine of evolution, and has been specially valuable in classification, as showing how nearly animals are related to each other. To classify animals and plants, in short, may be simply stated as a method of sorting them over and placing together those which have similar characters, just as in arranging a library we keep together books which relate to similar subjects. We may, for instance, make one general branch of history, a smaller branch of American history, and yet others relating to states, to counties, to cities and towns, and, most special of all, to particular families.
Discoveries in Physiology
The science of physiology differs from that of anatomy in dealing with the functions of life instead of with its forms. The study of these functions has gone on for many centuries, covering the various operations of motion, nutrition, respiration, nervous action, growth, and reproduction, with the many minor functions included under these. Though many of the facts of physiology were discovered in earlier centuries, the scientists of the nineteenth have been busy in adding to the list, and a number of important discoveries have been made. Prominent among these is that of anæsthesia, the discovery that by the inhalation of certain gases a state of temporary insensibility can be produced, lasting long enough to permit surgical and dental operations to be performed without pain; and that of antiseptical surgery, in which, by the employment of other chemical substances, wounds can be kept free from the action of deleterious substances, and surgical operations be performed without the perils formerly arising from inflammation,—the disease—producing germs and poisons being kept out.
Living Threads of the Brain
One of the great gains of the century, says Sir Michael Foster, from whom we have already quoted, is in our insight into nervous phenomena. “We now know that what takes place along a tiny thread we call a nerve fibre differs from that which takes place along its fellow threads; that differing nervous impulses travel along different nerve fibres; and that nervous and psychical events are the outcome of the clashing of nervous impulses as they sweep along the closely woven web of living threads, of which the brain is made. We have learned by experiment and observation that the pattern of the webdetermines the play of the impulses; and we can already explain many of the obscure problems, not only of nervous disease, but of nervous life, by an analysis, tracking out the devious and linked paths of the nervous threads.”
Brain Surgery
This observation links together the sciences of physiology and psychology, the latter the science of mental phenomena, the exact study of which largely belongs to the nineteenth century. Broad as this subject is, and much as has been done in it, few facts stand out with sufficient distinctness to call for special mention here. The most famous psychical experiments are those made on the brains of some of the animals below man, and especially on that of the monkey, by which the functions of the several sections of the brain have been to some extent mapped out, the important fact being discovered that each function is confined to a fixed locality in the brain, and with it the accordant fact that certain regions of the brain control the muscular movements of certain parts of the body. In consequence, a particular affection of the hand, foot, or other region has often been traced to a diseased condition of some known part of the brain, and the trouble has been removed by a surgical operation on that organ.
The Study of Man’s Past
The sciences last named refer specially to man, in whom they have been particularly studied. Other sciences relating to him exclusively are those of ethnology and anthropology, which belong almost solely to the nineteenth century. Ethnology, the study of the races of mankind, has been carefully and widely studied, and though the problems relating to it have not yet been solved, a very fair conception has been gained of the diversities and relations of mankind. Anthropology, embracing, as it does, archæology, has been prolific in discoveries. Archæological research has laid out before us the pathway of man through the ages and shown his gradual and steady development, through the successive periods of chipped stone and polished stone implements, of bronze and iron tools and weapons, with his gradual development of pottery, ornament, art, architecture, etc.
The most striking and notable fact in anthropological science is the total reversal of our ideas concerning the length of time man has dwelt upon the earth. The old limitation to a few thousand years, everywhere held at the beginning of the century, fails to reach back to a time when, as we now know, man had reached a considerable degree of civilization. Back of that we can trace him by his tools and his bones through a period many times more distant, leading back to the glacial age of geology and possibly to a much more remote era. Instead of man’s residence upon the earth being restricted to some 6,000 years, it probably reached back not less than 60,000, and possibly to a much earlier period.
Development of the Science of Medicine
Among the minor sciences, there is one that has deserved that name only within the past thirty or forty years, the science of medicine. Formerly it was an art only, and by no means a satisfactory one. Nothing was known of the cause of the most virulent and destructive diseases—the infectuous fevers, the plague, cholera, etc. And the treatment of these, and in fact of nearly all diseases, was wholly empirical, depending solely upon experiment, not at all upon scientific principles. Experience showed that certain drugs and chemical compounds produced certain effects upon the system, and upon this physicians depended, with no conception of the cause of diseases and little knowledge of the physiological action of medicines.
Pasteur and His Discoveries
This state of affairs was materially changed during the final third of the nineteenth century, as the result of an extensive series of observations, set in train in great part by Louis Pasteur, Professor of chemistry at the Sorbonne in Paris, who was in large measure the originator of the germ theory of disease. The discovery that the fermentation which produces alcohol is due to a microscopic organism, the yeast-plant, gave Pasteur the clue, and he soon was able to prove that other fermentations,—the lactic, acetic, and butyric,—are also due to the action of living forms. It had further been found that the putrefaction of animal substance was caused in the same way, and it has since been abundantly demonstrated that if these minute organisms can be kept out of animal and vegetable substances these may be preserved indefinitely. This fact has given rise to one of the most important industries of the century, the keeping of fruits, meats, etc., by the process of air-tight canning.
Pasteur next extended his observations to the silkworm, which was subject to an epidemic disease that had almost ruined the silk industry in France. Others before him had discovered what were supposed to be disease germs in the blood of these worms. He proved positively that these bacteria, as they are called, are the cause of the disease, and that infection could be prevented by proper precautions. From the insect Pasteur proceeded to the higher animals, and investigated the cause of splenic fever, a dangerous epidemic among farm cattle. This he also proved to be caused by a minute form of life, and that fowl cholera is due to still another form of micro-organism. At a later date he studied hydrophobia, which he traced to a similar cause, and for the cure of which he established the Pasteur Institute in 1886.
This was not the whole of Pasteur’s work. He discovered not only the cause of these diseases, but a system of vaccination by which they couldbe cured or prevented. By “cultivating” the bacteria in various ways, he succeeded in decreasing their dangerous properties, so that they would give the disease in a mild form,—acting in the same way as vaccination does in the case of small-pox, by enabling the animals to resist virulent attacks of the disease.