W. W. Ford,The Life and Work of Robert Koch, Bulletin of the Johns Hopkins Hospital, Dec. 1911, vol. 22.C. A. Herter,The Influence of Pasteur on Medical Science, Bulletin of the Johns Hopkins Hospital, Dec. 1903, vol. 14.E. O. Jordan,General Bacteriology(fourth edition, 1915).Charles C. W. Judd,The Life and Work of Lister, Bulletin of the Johns Hopkins Hospital, Oct. 1910, vol. 21.Stephen Paget,Pasteur and After Pasteur.W. T. Sedgwick,Principles of Sanitary Science.René Vallery-Radot,Life of Pasteur.
W. W. Ford,The Life and Work of Robert Koch, Bulletin of the Johns Hopkins Hospital, Dec. 1911, vol. 22.
C. A. Herter,The Influence of Pasteur on Medical Science, Bulletin of the Johns Hopkins Hospital, Dec. 1903, vol. 14.
E. O. Jordan,General Bacteriology(fourth edition, 1915).
Charles C. W. Judd,The Life and Work of Lister, Bulletin of the Johns Hopkins Hospital, Oct. 1910, vol. 21.
Stephen Paget,Pasteur and After Pasteur.
W. T. Sedgwick,Principles of Sanitary Science.
René Vallery-Radot,Life of Pasteur.
In his laudation of the nineteenth century Alfred Russel Wallace ventured to enumerate the chief inventions of that period: (1) Railways; (2) steam navigation; (3) electric telegraphs; (4) the telephone; (5) friction matches; (6) gas-lighting; (7) electric-lighting; (8) photography; (9) the phonograph; (10) electric transmission of power; (11) Röntgen rays; (12) spectrum analysis; (13) anæsthetics; (14) antiseptic surgery. All preceding centuries—less glorious than the nineteenth—can claim but seven or eight capital inventions: (1) Alphabetic writing; (2) Arabic numerals; (3) the mariner's compass; (4) printing; (5) the telescope; (6) the barometer and thermometer; (7) the steam engine. Similarly, to the nineteenth century thirteen important theoretical discoveries are ascribed, to the eighteenth only two, and to the seventeenth five.
Of course the very purpose of these lists—namely, to compare the achievements of one century with those of other centuries—inclines us to view each invention as an isolated phenomenon, disregarding its antecedents and its relation to contemporary inventions. Studied in its development, steam navigation is but an application of one kind of steam engine, and, moreover, must be viewed as aphase in the evolution of navigation since the earliest times. Like considerations would apply to railways, antiseptic surgery, or friction matches. The nineteenth-century inventor of the friction match was certainly no more ingenious (considering the means that chemistry had put at his disposal) than many of the savages who contributed by their intelligence to methods of producing, maintaining, and using fire. In fact, as we approach the consideration of prehistoric times it becomes difficult to distinguish inventions from the slow results of development—in metallurgy, tool-making, building, pottery, war-gear, weaving, cooking, the domestication of animals, the selection and cultivation of plants. Moreover, it is scarcely in the category of invention that the acquisition of alphabetic writing or the use of Arabic numerals properly belongs.
These and other objections, such as the omission of explosives, firearms, paper, will readily occur to the reader. Nevertheless, these lists, placed side by side with the record of theoretic discoveries, encourage the belief that, more and more, sound theory is productive of useful inventions, and that henceforth it must fall to scientific endeavor rather than to lucky accident to strengthen man's control over Nature. Even as late as the middle of the nineteenth century accident and not science was regarded as the fountain-head of invention, and the view that a knowledge of the causes and secret motions of things would lead to "the enlarging of the bounds of human empire to the effecting of all things possible" was scouted as the idle dream of a doctrinaire.
In the year 1896 three important advances weremade in man's mastery of his environment. These are associated with the names of Marconi, Becquerel, and Langley. It was in this year that the last-named, long known to the scientific world for his discoveries in solar physics, demonstrated in the judgment of competent witnesses the practicability of mechanical flight. This was the result of nine years' experimentation. It was followed by several more years of fruitful investigation, leading to that ultimate triumph which it was given to Samuel Pierpont Langley to see only with the eye of faith.
The English language has need of a new word ("plane") to signify the floating of a bird upon the wing with slight, or no, apparent motion of the wings (planer,schweben).To hoverhas other connotations, whileto soaris properly to fly upward, and not to hang poised upon the air. The miracle of a bird's flight, that steady and almost effortless motion, had interested Langley intensely—as had also the sun's radiation—from the years of his childhood. The phenomenon (the way of an eagle in the air) has always, indeed, fascinated the human imagination and at the same time baffled the comprehension. The skater on smooth ice, the ship riding at sea, or even the fish floating in water, offers only an incomplete analogy; for the fish has approximately the same weight as the water it displaces, while a turkey buzzard of two or three pounds' weight will circle by the half-hour on motionless wing upheld only by the thin medium of the air.
In 1887, prior to his removal to Washington as Secretary of the Smithsonian Institution, Langley began his experiments in aerodynamics at the oldobservatory in Allegheny—now a part of the city of Pittsburgh. His chief apparatus was a whirling table, sixty feet in diameter, and with an outside speed of seventy miles an hour. This was at first driven by a gas engine,—ironically named "Automatic,"—for which a steam engine was substituted in the following year. By means of the whirling table and a resistance-gauge (dynamometer chronograph) Langley studied the effect of the air on planes of varying lengths and breadths, set at varying angles, and borne horizontally at different velocities. At times he substituted stuffed birds for the metal planes, on the action of which under air pressure his scientific deductions were based. In 1891 he published the results of his experiments. These proved—in opposition to the teaching of some very distinguished scientists—that the force required to sustain inclined planes in horizontal locomotion through the air diminishes with increased velocity (at least within the limits of the experiment). Here a marked contrast is shown between aerial locomotion on the one hand, and land and water locomotion on the other; "whereas in land or marine transport increased speed is maintained only by a disproportionate expenditure of power, within the limits of experiment in suchaerial horizontal transport, the higher speeds are more economical of power than the lower ones." Again, the experiments demonstrated that the force necessary to maintain at high velocity an apparatus consisting of planes and motors could be produced by means already available. It was found, for example, that one horse-power rightly applied is sufficient to maintain a plane of two hundred pounds inhorizontal flight at a rate of about forty-five miles an hour. Langley had in fact furnished experimental proof that the aerial locomotion of bodies many times heavier than air was possible. He reserved for further experimentation the question of aerodromics, the form, ascent, maintenance in horizontal position, and descent of an aerodrome (ἀεροδρόμος, traversing the air), as he called the prospective flying machine. He believed, however, that the time had come for seriously considering these things, and intelligent physicists, who before the publication of Langley's experiments had regarded all plans of aerial navigation as utopian, soon came to share his belief. According to Octave Chanute there was in Europe in 1889 utter disagreement and confusion in reference to fundamental questions of aerodynamics. He thought Langley had given firm ground to stand upon concerning air resistances and reactions, and that the beginning of the solution of the problem of aerial navigation would date from the American scientist's experiments in aerodynamics.
Very early in his investigations Langley thought he received through watching the anemometer a clue to the mystery of flight. Observations, begun at Pittsburgh in 1887 and continued at Washington in 1893, convinced him that the course of the wind is "a series of complex and little-known phenomena," and that a wind to which we may assign a mean velocity of twenty or thirty miles an hour, even disregarding the question of strata and currents, is far from being a mere mass movement, and consists of pulsations varying both in rate and direction from second to second. If this complexity is revealed by the stationaryanemometer—which may register a momentary calm in the midst of a gale—how great a diversity of pressure must exist in a large extent of atmosphere. Thisinternal work of the windwill lift the soaring bird at times to higher levels, from which without special movement of the wings it may descend in the very face of the wind's general course.
From the beginning, however, of his experiments Langley had sought to devise a successful flying machine. In 1887 and the following years he constructed about forty rubber-driven models, all of which were submitted to trial and modification. From these tests he felt that he learned much about the conditions of flight in free air which could not be learned from the more definitely controlled tests with simple planes on the whirling table. His essential object was, of course, to reduce the principles of equilibrium to practice. Besides different forms and sizes he tried various materials of construction, and ultimately various means of propulsion. Before he could test his larger steam-driven models, made for the most part of steel and weighing about one thousand times as much as the air displaced, Langley spent many months contriving and constructing suitable launching apparatus. The solution of the problem of safe descent after flight he in a sense postponed, conducting his experiments from a house-boat on the Potomac, where the model might come down without serious damage.
THE FIRST SUCCESSFUL HEAVIER-THAN-AIR FLYING MACHINEA photograph taken at the moment of launching Langley's aerodrome May 6, 1896
It was on May 6, 1896 (the anniversary of which date is now celebrated as Langley Day), that the success was achieved which all who witnessed it considered decisive of the future of mechanical flight. The whole apparatus—steel frame, miniature steam engine, smoke stack, condensed-air chamber, gasoline tank, wooden propellers, wings—weighed about twenty-four pounds. There was developed a steam pressure of about 115 pounds, and the actual power was nearly one horse-power. At a given signal the aeroplane was released from the overhead launching apparatus on the upper deck of the house-boat. It rose steadily to an ultimate height of from seventy to a hundred feet. It circled (owing to the guys of one wing being loose) to the right, completing two circles and beginning a third as it advanced; so that the whole course had the form of a spiral. At the end of one minute and twenty seconds the propellers began to slow down owing to the exhaustion of fuel. The aeroplane descended slowly and gracefully, appearing to settle on the water. It seemed to Alexander Graham Bell that no one could witness this interesting spectacle, of a flying machine in perfect equilibrium, without being convinced that the possibility of aerial flight by mechanical means had been demonstrated. On the very day of the test he wrote to the Académie des Sciences that there had never before been constructed, so far as he knew, a heavier-than-air flying machine, or aerodrome, which could by its own power maintain itself in the air for more than a few seconds.
Langley felt that he had now completed the work in this field which properly belonged to him as a scientist—"the demonstration of the practicability of mechanical flight"—and that the public might look to others for its development and commercial exploitation. Like Franklin and Davy he declinedto take out patents, or in any way to make money from scientific discovery; and like Henry, the first Secretary of the Smithsonian Institution (to whom the early development of electro-magnetic machines was due), he preferred to be known as a scientist rather than as an inventor.
Nevertheless, Langley's desire to construct a large, man-carrying aeroplane ultimately became irresistible. Just before the outbreak of the Spanish War in 1898 he felt that such a machine might be of service to his country in the event of hostilities that seemed to him imminent. The attention of President McKinley was called to the matter, and a joint commission of Army and Navy officers was appointed to make investigation of the results of Professor Langley's experiments in aerial navigation. A favorable report having been made by that body, the Board of Ordnance and Fortification recommended a grant of fifty thousand dollars to defray the expenses of further research. Langley was requested to undertake the construction of a machine which might lead to the development of an engine of war, and in December, 1898, he formally agreed to go on with the work.
He hoped at first to obtain from manufacturers a gasoline engine sufficiently light and sufficiently powerful for a man-carrying machine. After several disappointments, the automobile industry being then in its infancy, he succeeded in constructing a five-cylinder gasoline motor of fifty-two horse-power and weighing only about a hundred and twenty pounds. He also constructed new launching apparatus. After tests with superposed sustaining surfaces, he adhered to the "single-tier plan." There is interesting evidence that in 1900 Langley renewed his study of the flight of soaring birds, the area of their extended wing surface in relation to weight, and the vertical distance between the center of pressure and the center of gravity in gulls and different species of buzzards. He noted among other things that the tilting of a wing was sufficient to bring about a complete change of direction.
By the summer of 1903 two new machines were ready for field trials, which were undertaken from a large house-boat, especially constructed for the purpose and then moored in the mid-stream of the Potomac about forty miles below Washington. The larger of these two machines weighed seven hundred and five pounds and was designed to carry an engineer to control the motor and direct the flight. The motive power was supplied by the light and powerful gasoline engine already referred to. The smaller aeroplane was a quarter-size model of the larger one. It weighed fifty-eight pounds, had an engine of between two and a half and three horse-power, and a sustaining surface of sixty-six square feet.
This smaller machine was tested August 8, 1903, the same launching apparatus being employed as with the steam-driven models of 1896. In spite of the fact that one of the mechanics failed to withdraw a certain pin at the moment of launching, and that some breakage of the apparatus consequently occurred, the aeroplane made a good start, and fulfilled the main purpose of the test by maintaining a perfect equilibrium. After moving about three hundred and fifty feet in a straight course it wheeled a quarter-circle to the right, at the same time descendingslightly, the engine slowing down. Then it began to rise, moving straight ahead again for three or four hundred feet, the propellers picking up their former rate. Once more the engine slackened, but, before the aeroplane reached the water, seemed to regain its normal speed. For a third time the engine slowed down, and, before it recovered, the aeroplane had touched the water. It had traversed a distance of one thousand feet in twenty-seven seconds. One of the workmen confessed that he had poured into the tank too much gasoline. This had caused an overflow into the intake pipe, which in turn interfered with the action of a valve.
The larger aeroplane with the engineer Manly on board was first tested on October 7 of the same year, but the front guy post caught in the launching car and the machine plunged into the water a few feet from the house-boat. In spite of this discouraging mishap the engineers and others present felt confidence in the aeroplane's power to fly. What would to-day be regarded by an aeronaut as a slight setback seemed at that moment like a tragic failure. The fifty thousand dollars had been exhausted nearly two years previously; Professor Langley had made as full use as seemed to him advisable of the resources put at his disposal by the Smithsonian Institution; the young men of the press, for whom the supposed aberration of a great scientist furnished excellent copy, were virulent in their criticisms. Manly made one more heroic attempt under very unfavorable conditions at the close of a winter's day (December 8, 1903). Again difficulty occurred with the launching gear, the rear wings and rudder being wrecked before the aeroplane was clear of the ways. The experiments were now definitely abandoned, and the inventor was overwhelmed by the sense of failure, and still more by the skepticism with which the public had regarded his endeavors.
In 1905 an account of Langley's aeroplane appeared in the Bulletin of the Italian Aeronautical Society. Two years later this same publication in an article on a new Blériot aeroplane said: "The Blériot IV in the form of a bird ... does not appear to give good results, perhaps on account of the lack of stability, and Blériot, instead of trying some new modification which might remedy such a grave fault, laid it aside and at once began the construction of a new type, No. V, adopting purely and simply the arrangement of the American, Langley, which offers a good stability." In the summer of 1907 Blériot obtained striking results with this machine, the launching problem having been solved in the previous year—the year of Langley's death—by the use of wheels which permitted the aeroplane to get under way by running along the ground under its own driving power. The early flights with No. V were made at a few feet from the ground, and the clever French aviator could affect the direction of the machine by slightly shifting his position, and even had skill to bring it down by simply leaning forward. By the use of the steering apparatus he circled to the right or to the left with the grace of a bird on the wing. When, on July 25, 1909, Blériot crossed the English Channel in his monoplane, all the world knew that man's conquest of the air was afait accompli.
About three years after Langley's death the Board of Regents of the Smithsonian Institution established the Langley Medal for investigations in aerodromics in its application to aviation. The first award went (1909) to Wilbur and Orville Wright, the second (1913) to Mr. Glenn H. Curtiss and M. Gustave Eiffel. On the occasion of the presentation of the medals of the second award—May 6, 1913—the Langley Memorial Tablet, erected in the main vestibule of the Smithsonian building, was unveiled by the scientist's old friend, Dr. John A. Brashear. In the words of the present Secretary of the Institution, the tablet represents Mr. Langley seated on a terrace where he has a clear view of the heavens, and, in a meditative mood, is observing the flight of birds, while in his mind he sees his aerodrome soaring above them.
The lettering of the tablet is as follows:—
SAMUEL PIERPONT LANGLEY1834-1906
SECRETARY OF THE SMITHSONIAN INSTITUTION1887-1906
DISCOVERED THE RELATIONS OF SPEEDAND ANGLE OF INCLINATION TO THELIFTING POWER OF SURFACES WHENMOVING IN AIR
"I have brought to a close the portion of the work which seemed to be especially mine, the demonstration of the practicability of mechanical flight.""The great universal highway overhead is now soon to be opened."—Langley, 1897.
"I have brought to a close the portion of the work which seemed to be especially mine, the demonstration of the practicability of mechanical flight."
"The great universal highway overhead is now soon to be opened."—Langley, 1897.
A still more fitting tribute to the memory of the great inventor came two years later from a successful aviator. In the spring of 1914 Mr. Glenn H. Curtiss was invited to send apparatus to Washington for the Langley Day Celebration. He expressed the desire to put the Langley aeroplane itself in the air. The machine was taken to the Curtiss Aviation Field at Keuka Lake, New York. Langley's method of launching had been proved practical, but Curtiss finally decided to start from the water, and accordingly fitted the aeroplane with hydroaeroplane floats. In spite of the great increase in weight involved by this addition, the Langley aeroplane, under its own power plant, skimmed over the wavelets, rose from the lake, and soared gracefully in the air, maintaining its equilibrium, on May 28, 1914, over eight years after the death of its designer. When furnished with an eighty horse-power motor, more suited to its increased weight, the aerodrome planed easily over the water in more prolonged flight. In the periodical publications of June, 1914, may be read the eloquent announcement: "Langley's Folly Flies."
Alexander Graham Bell, Experiments in Mechanical Flight,Nature, May 28, 1896.Alexander Graham Bell, The Pioneer Aerial Flight,Scientific American, Supplement, Feb. 26, 1910.S. P. Langley,Experiments in Aerodynamics.S. P. Langley, The "Flying Machine,"McClure's, June, 1897 (illustrated).Langley Memoir on Mechanical Flight, Smithsonian Contributions to Knowledge, vol. 27, no. 3 (illustrated).Scientific American, Jan. 13, 1912, A Memorial Honor to a Pioneer Inventor.The Smithsonian Institution 1846-1896. The History of its First Half-Century, edited by G. B. Goode.A. F. Zahm,The First Man-carrying Aeroplane capable of Sustained Free Flight, Annual Report of the Smithsonian Institution, 1914 (illustrated).
Alexander Graham Bell, Experiments in Mechanical Flight,Nature, May 28, 1896.
Alexander Graham Bell, The Pioneer Aerial Flight,Scientific American, Supplement, Feb. 26, 1910.
S. P. Langley,Experiments in Aerodynamics.
S. P. Langley, The "Flying Machine,"McClure's, June, 1897 (illustrated).
Langley Memoir on Mechanical Flight, Smithsonian Contributions to Knowledge, vol. 27, no. 3 (illustrated).
Scientific American, Jan. 13, 1912, A Memorial Honor to a Pioneer Inventor.
The Smithsonian Institution 1846-1896. The History of its First Half-Century, edited by G. B. Goode.
A. F. Zahm,The First Man-carrying Aeroplane capable of Sustained Free Flight, Annual Report of the Smithsonian Institution, 1914 (illustrated).
The untrained mind, reliant on so-called facts and distrustful of mere theory, inclines to think of truth as fixed rather than progressive, static rather than dynamic. It longs for certainty and repose, and has little patience for any authority that does not claim absolute infallibility. Many a man of the world is bewildered to find Newton's disciples building upon or refuting the teachings of the master, or to learn that Darwin's doctrine is itself subject to the universal law of change and development. Though in ethics and religion the older order changes yielding place to new, and the dispensation of an eye for an eye and a tooth for a tooth finds its fulfilment and culmination in a dispensation of forbearance and non-resistance of evil, still many look upon the overthrow of any scientific theory not as a sign of vitality and advance, but as a symptom of the early dissolution or at least of the bankruptcy of science. It is not surprising, therefore, that the public regard the scientific hypothesis with a kind of contempt; for a hypothesis (ὑπόθεσις, foundation, supposition) is necessarily ephemeral. When disproved, it is shown to have been a false supposition; when proved, it is no longer hypothetic.
Yet a page from the history of science should indicate that hypotheses play a rôle in experimentalscience and lead to results that no devotee of facts and scorner of mere theory can well ignore.
In 1895 Sir William Ramsay, who in the previous year had discovered an inert gas, argon, in the atmosphere, identified a second inert gas (obtained from minerals containing uranium and thorium) as helium (ἥλιος, sun), an element previously revealed by spectrum analysis as a constituent of the sun. In the same year Röntgen, while experimenting with the rays that stream from the cathode in a vacuum tube, discovered new rays (which he called X-rays) possessed of wonderful photographic power. At the beginning of 1896 Henri Becquerel, experimenting on the supposition, or hypothesis, that the emission of rays was associated with phosphorescence, tested the photographic effects of a number of phosphorescent substances. He exposed, among other compounds, crystals of the double sulphate of uranium and potassium to sunlight and then placed upon the crystals a photographic plate wrapped in two thicknesses of heavy black paper. The outline of the phosphorescent substance was developed on the plate. An image of a coin was obtained by placing it between uranic salts and a photographic plate. Two or three days after reporting this result Becquerel chanced (the sunlight at the time seeming to him too intermittent for experimentation) to put away in the same drawer, and in juxtaposition, a photographic plate and these phosphorescent salts. To his surprise he obtained a clear image when the plate was developed. He now assumed the existence of invisible rays similar to X-rays. They proved capable of passing through sheets of aluminum and of copper, and of discharging electrified bodies. Days elapsed without any apparent diminution of the radiation. On the supposition that the rays might resemble light he tried to refract, reflect, and polarize them; but this hypothesis was by the experiments of Rutherford, and of Becquerel himself, ultimately overthrown. In the mean time the French scientist obtained radiations from metallic uranium and from uranous salts. These, in contrast with the uranic salts, are non-phosphorescent. Becquerel's original hypothesis was thus overthrown. Radiation is a property inherent in uranium and independent both of light and of phosphorescence.
On April 13 and April 23 (1898) respectively Mme. Sklodowska Curie and G. C. Schmidt published the results of their studies of the radiations of the salts of thorium. Each of these studies was based on the work of Becquerel. Mme. Curie examined at the same time the salts of uranium and a number of uranium ores. Among the latter she made use of the composite mineral pitchblende from the mines of Joachimsthal and elsewhere, and found that the radiations from the natural ores are more active than those from pure uranium. This discovery naturally led to further investigation, on the assumption that pitchblende contains more than one radioactive substance. Polonium, named by Mme. Curie in honor of her native country, was the third radioactive element to be discovered. In the chemical analysis of pitchblende made by Mme. Curie (assisted by M. Curie) polonium was found associated with bismuth. Radium, also discovered in this analysis of 1898, was associated with barium. Mme. Curie succeeded in obtaining the pure chloride ofradium and in determining the atomic weight of the new element. There is (according to Soddy) about one part of radium in five million parts of the best pitchblende, but the new element is about one million times more radioactive than uranium. It was calculated by M. Curie that the energy of one gram of radium would suffice to lift a weight of five hundred tons to a height of one mile. After discussing the bearing of the discovery of radioactivity on the threatened exhaustion of the coal supply Soddy writes enthusiastically: "But the recognition of the boundless and inexhaustible energy of Nature (and the intellectual gratification it affords) brightens the whole outlook of the twentieth century." The element yields spontaneously radium emanation without any apparent diminution of its own mass. In 1899 Debierne discovered, also in the highly complex pitchblende, actinium, which has proved considerably less radioactive than radium. During these investigations M. and Mme. Curie, M. Becquerel, and those associated with them were influenced by the hypothesis that radioactivity is anatomic propertyof radioactive substances. This hypothesis came to definite expression in 1899 and again in 1902 through Mme. Curie.
In the latter year the physicist E. Rutherford and the chemist F. Soddy, while investigating the radioactivity of thorium in the laboratories of McGill University, Montreal, were forced to recognize that thorium continuously gives rise to new kinds of radioactive matter differing from itself in chemical properties, in stability, and in radiant energy. They concurred in the view held by all the most prominentworkers in this subject, namely, that radioactivity is an atomic phenomenon. It is not molecular decomposition. They declared that the radioactive substances must be undergoing a spontaneous transformation. The daring nature of this hypothesis and its likelihood to revolutionize physical science is brought home to one by recalling that three decades previously an eminent physicist had said that "though in the course of ages catastrophes have occurred and may yet occur in the heavens, though ancient systems may be dissolved and new systems evolved out of their ruins, the molecules [atoms] out of which these systems are built—the foundation stones of the material universe—remain unbroken and unworn."
In 1903 Rutherford and Soddy stated definitely their hypothesis, generally known as the "Transformation Theory," that the atoms of radioactive substances suffer spontaneous disintegration, a process unaffected by great changes of temperature (or by physical or chemical changes of any kind at the disposal of the experimenter) and giving rise to new radioactive substances differing in chemical (and physical) properties from the parent elements. The radiations consist of α particles (atoms of helium minus two negative electrons), β particles, or electrons (charges of negative electricity), and γ rays, of the nature of Röntgen rays and light but of very much shorter wave length and of very great penetrating power. It is by the energy inherent in the atom of the radioactive substance that the radiations are ejected, sometimes, in the case of the γ rays, with velocity sufficient to penetrate two feet of lead. It is through these radiations that spontaneous transformationtakes place. After ten years of further investigation Rutherford stated that this hypothesis affords a satisfactory explanation of all radioactive phenomena, and gives unity to what without it would seem disconnected facts. Besides accounting for old experimental results it suggests new lines of work and even enables one to predict the outcome of further investigation. It does not really contradict, as some thought might be the case, the principle of the conservation of energy. The atom, to be sure, can no longer be considered the smallest unit of matter, as the mass of a β particle is approximately one seventeen-hundredths that of an atom of hydrogen. Still the new hypothesis is a modification and not a contradiction of the atomic theory.
The assumption that the series of radioactive substances is due, not to such molecular changes as chemistry had made familiar, but to a breakdown of the atom seemed to Rutherford in 1913 at least justified by the results of the investigators whose procedure had been dictated by that hypothesis. He set forth in tables these results (since somewhat modified), indicating after the name of each radioactive substance the nature of the radiation through the emission of which the element is transformed into the next-succeeding member of its series.
Even a glance at this long list of new elements reveals certain analogies between one series of transformations and another. Each series contains an emanation, or gas, which through the loss of α particles is transformed into the next following member of the series. Continuing the comparison in either direction, up or down the lists, one could readily detect other analogies.
There is some ground for thinking that lead is the end product of the Uranium series. To reverse the process of the transformation and produce radium from the base metal lead would be an achievement greater than the vaunted transmutations of the alchemists. Although that seems beyond the reach of possibility, the idea has stirred the imagination of more than one scientist. "The philosopher's stone," writes Soddy, "was accredited the power not only of transmuting the metals, but of actingas the elixir of life. Now, whatever the origin of this apparently meaningless jumble of ideas may have been, it is really a perfect and but very slightly allegorical expression of the actual present views we hold to-day." Again, it is conjectured that bismuth is the end-product of the thorium series. The presence of the results of atomic disintegration (like lead and helium) has proved of interest to geology and other sciences as affording a clue to the age of the rocks in which they are found deposited.
Before Rutherford, Mme. Curie, and others especially interested in radioactive substances, assumed that atoms are far different from the massy, hard, impenetrable particles that Newton took for granted, Sir J. J. Thomson and his school were studying theconstitution of the atom from another standpoint but with somewhat similar results. This great physicist had proved that cathode rays are composed not of negatively charged molecules, as had been supposed, but of much smaller particles or corpuscles. Wherever, as in the vacuum tube, these electrons appear, the presence of positively charged particles can also be demonstrated. It is manifest that the atom, instead of being the ultimate unit of matter, is a system of positively and negatively charged particles. Rutherford in the main concurred in this view, though differing from Sir J. J. Thomson as to the arrangement of corpuscles within the atom. Let it suffice here to state that Rutherford assumes that the greater mass of the atom consists of negatively charged particles rotating about a positive nucleus. The surrounding electrons render the atom electrically neutral.
This corpuscular theory of matter may throw light on the laws of chemical combination. The so-called chemical affinity between two atoms of such and such valencies, which Davy and others since his time had regarded as essentially an electrical phenomenon, seems now to admit of more definite interpretation. Each atom is negatively or positively charged according to the addition or subtraction of electrons. Chemical composition takes place between atoms the charges of which are of opposite sign, and valency depends on the number of unit charges of electricity. Moreover, the electrical theory of matter lends support to the hypothesis that there is a fundamental unitary element underlying all the so-called elements. The fact that elements fall into groups and that their chemical properties vary with their atomic weights long ago suggested this assumption of a primitive matter,protyl, from which all other substances were derived. In the light of the corpuscular theory as well as of the transformation theory it seems possible that the helium atom and the negative corpuscle will offer a clue to the genesis of the elements.
What is to be learned from this rapid sketch, of the discovery of the radioactive substances, concerning the nature and value of scientific hypothesis? For one thing, the scientific hypothesis is necessary to the experimenter. The mind runs ahead of and guides the experiment. Again, the hypothesis suggests new lines of research, enables one in some cases to anticipate the outcome of experiment, and may be abundantly justified by results. "It is safe to say," writes Rutherford, "that the rapidity of growth of accurate knowledge of radioactive phenomena has been largely due to the influence of the disintegration theory." The valid hypothesis serves to explain facts, leads to discovery, and does not conflict with known facts or with verified generalizations, though, as we have seen, it may modify other hypotheses. Those who support a hypothesis should bring it to the test of rigid verification, avoiding skepticism, shunning credulity. Even a false assumption, as we have seen, may prove valuable when carefully put to the proof.
The layman's distrust of the unverified hypothesis is in the main wholesome. It is a duty not to believe it, not to disbelieve it, but to weigh judicially the evidence for and against. The fact that assumption plays a large part in our mental attitude toward practical affairs should make us wary of contesting the legitimacy of scientific hypotheses.
No one would deny the right of forming a provisional assumption to the intelligence officer interpreting a cipher, or to the detective unravelling the mystery of a crime. The first assumes that the message is in a certain language, and, perhaps, that each symbol employed is the equivalent of a letter, his assumption is put to the proof of getting a reasonable and consistent meaning from the cipher. The detective assumes a motive for the crime, or the employment of certain means of escape; even if his assumption does not clear up the mystery, it may have value as leading to a new and more adequate assumption.
Henri Poincaré has pointed out that one of the most dangerous forms of hypothesis is the unconscious hypothesis. It is difficult to prove or disprove because it does not come to clear statement. The alleged devotee of facts and of things as they are, in opposing the assumptions of an up-to-date science, is often, unknown to himself, standing on a platform of outworn theory, or of mere vulgar assumption. For example, when Napoleon was trying to destroy the commercial wealth of England at the beginning of the nineteenth century, he unconsciously based his procedure on an antiquated doctrine of political economy. For him the teachings of Adam Smith and Turgot were idle sophistries. "I seek," he said to his Minister of Finance, "the good that is practical, not the ideal best: the world is very old, we must profit by its experience; it teaches that old practices are worth more than new theories: you are not the only one who knows trade secrets." We are not here especially concerned with the question of whether Napoleon was or was not pursuing the bestmeans of breaking down English credit. He did try to prevent the English from exchanging exports for European gold, while permitting imports in the hope of depleting England of gold. But in pursuing this policy he thought he was proceeding on the ground of immemorial practice, while he was merely pitting the seventeenth-century doctrine of Locke against the doctrine of Adam Smith which had superseded it.
According to one scientific hypothesis, "Species originated by means of natural selection, or, through the preservation of favored races in the struggle for life." This assumption was rightly subjected to close scrutiny in 1859 and the years following. The ephemeral nature of the vast majority of hypotheses and the danger to progress of accepting an unverified assumption justify the demand for demonstrative evidence. The testimony having been examined, it is our privilege to state and to support the opposing hypothesis. It was thus that the hypothesis that the planets move in circular orbits, recommended by its simplicity and æsthetic quality, was forced to give way to the hypothesis of elliptical orbits. Newton's hypothesis that light is due to particles emitted by all luminous bodies yielded, at least for the time, to the theory of light vibrations in an ether pervading all space. The path of scientific progress is strewn with the ruins of overthrown hypotheses. Many of the defeated assumptions have been merely implicit errors of the man in the street, and they are overthrown not by facts alone, but by new hypotheses verified by facts and leading to fresh discoveries.
According to John Stuart Mill, "It appears ... to be a condition of a genuinely scientific hypothesis,that it be not destined always to remain an hypothesis, but be of such a nature as to be either proved or disproved by that comparison with observed facts which is termed Verification." This statement is of value in confirming the general distrust ofmerehypothesis, and in distinguishing between the unverified and unverifiable presupposition and the legitimate assumption which through verification may become established doctrine.
J. Cox,Beyond the Atom, 1913 (Cambridge Manuals of Science and Literature).R. K. Duncan,The New Knowledge, 1905.H. Poincaré,Science and Hypothesis.E. Rutherford,Radioactive Substances and their Radiations.F. Soddy,The Interpretation of Radium.F. Soddy,Matter and Energy(Home University Library).Sir William A. Tilden,Progress of Scientific Chemistry in our Own Time, 1913.
J. Cox,Beyond the Atom, 1913 (Cambridge Manuals of Science and Literature).
R. K. Duncan,The New Knowledge, 1905.
H. Poincaré,Science and Hypothesis.
E. Rutherford,Radioactive Substances and their Radiations.
F. Soddy,The Interpretation of Radium.
F. Soddy,Matter and Energy(Home University Library).
Sir William A. Tilden,Progress of Scientific Chemistry in our Own Time, 1913.
Psychology, or the science of mental life as revealed in behavior, has been greatly indebted to physiologists and to students of medicine in general. Any attempt to catalogue the names of those who have approached the study of the mind from the direction of the natural sciences is liable to prove unsatisfactory, and a brief list is sure to entail many important omissions. The mention of Locke, Cheselden, Hartley, Cabanis, Young, Weber, Gall, Müller, Du Bois-Reymond, Bell, Magendie, Helmholtz, Darwin, Lotze, Ferrier, Goltz, Munk, Mosso, Maudsley, Carpenter, Galton, Hering, Clouston, James, Janet, Kraepelin, Flechsig, and Wundt will, however, serve to remind us of the richness of the contribution of the natural sciences to the so-called mental science. Indeed, physiology would be incomplete unless it took account of the functions of the sense organs, of the sensory and motor nerves, of the brain with its association areas, as well as the expression of the emotions, and the changes of function accompanying the development of the nervous system, from the formation of the embryo till physical dissolution, and from species of the simplest to those of the most complex organization.
At the beginning of the nineteenth century the French physician Cabanis was disposed to identify human personality with mere nervous organizationreacting to physical impressions, and to look upon the brain as the organ for the production of mind. He soon, however, withdrew from this extreme position and expressed his conviction of the existence of an immortal spirit apart from the body. One might say that the brain is the instrument through which the mind manifests itself rather than the organ by which mind is excreted. Even so, it must be agreed that the relation between the psychic agent and the physical instrument is so close that physiology must take heed of mental phenomena and that psychology must not ignore the physical concomitants of mental processes. Hence arises a new branch of natural science, physiological psychology, or, as Fechner (1860), the disciple of Weber, called it, psycho-physics.
Through this alliance between the study of the mind and the study of bodily functions the intelligence of the lower animals and its survival value, the mental growth of the child, mental deterioration in age and disease, and the psychological endowments of special classes or of individuals, became subjects for investigation. Now human psychology is recognized as contributing to various branches of anthropology, or the general study of man.
Wilhelm Wundt, who, as already implied, had approached the study of the mind from the side of the natural sciences, established in 1875 at the University of Leipzig the first psycho-physical institute for the experimental study of mental phenomena. His express purpose was to analyze the content of consciousness into its elements, to examine these elements in their qualitative and quantitative differences, and to determine with precision the conditions of their existence and succession. Thus science after contemplating a wide range of outer phenomena—plants, animals, earth's crust, heavenly bodies, molecules and atoms—turns its attention with keen scrutiny inward on the thinking mind, the subjective process by which man becomes cognizant of all objective things.
The need of expert study of the human mind as the instrument of scientific discovery might have been inferred from the fact that the physicist Tyndall read before the British Association in 1870 a paper on the Scientific Use of the Imagination, in which he spoke of the imagination as the architect of physical theory, cited Newton, Dalton, Davy, and Faraday as affording examples of the just use of this creative power of the mind, and quoted a distinguished chemist as identifying the mental process of scientific discovery with that of artistic production. Tyndall even chased the psychologists in their own field and stated that it was only by the exercise of the imagination that we could ascribe the possession of mental powers to our fellow creatures. "You believe that in society you are surrounded by reasonable beings like yourself.... What is your warrant for this conviction? Simply and solely this: your fellow-creatures behave as if they were reasonable."
On the traces of this brilliant incursion of the natural philosopher into the realm of mental science, later psychologists must follow but haltingly. Just as in the history of physics a long series of studies intervened between Bacon's hypothesis that heat is a kind of motion (1620) and Tyndall's own work,Heat as a Mode of Motion(1863), so must manypsychological investigations be made before an adequate psychology of scientific discovery can be formulated. It may ultimately prove that the passages in which Tyndall and other scientists speak of scientificimaginationwould read as well if for this term, intuition, inspiration, unconscious cerebration, or even reason were substituted.
At first glance it would seem that the study of the sensory elements of consciousness, motor, tactile, visual, auditory, olfactory, gustatory, thermal, internal, pursued for the last half century by the experimental method, would furnish a clue to the nature of the imagination. A visual image, or mental picture, is popularly taken as characteristic of the imaginative process. In fact, the distinguished psychologist William James devotes the whole of his interesting chapter on the imagination to the discussion of different types of imagery. The sensory elements of consciousness are involved, however, in perception, memory, volition, reason, and sentiment, as they are in imagination. They have been recognized as fundamental from antiquity. Nothing is in the intellect which was not previously in the senses. To be out of one's senses is to lack the purposive guidance of the intelligence.
The psychology of individuals and groups shows startling differences in the kind and vividness of imagery. Many cases are on record where the mental life is almost exclusively in visual, in auditory, or in motor terms. One student learns a foreign language by writing out every word and sentence; another is wholly dependent on hearing them spoken; a third can recall the printed page with an almost photographic vividness. The history of literature and art furnishes us with illustrations of remarkable powers of visualization. Blake and Fromentin were able to reproduce in pictures scenes long retained in memory. The latter recognized that his painting was not an exact reproduction of what he had seen, but that it was none the less artistic because of the selective influence that his mind had exerted on the memory image. Wordsworth at times postponed the description of a scene that appealed to his poetic fancy with the express purpose of blurring the outlines, but enhancing the personal factor. Goethe had the power to call up at will the form of a flower, to make it change from one color to another and to unfold before his mind's eye. Professor Dilthey has collected many other records of the hallucinatory clearness of the visual imagery of literary artists.
On the other hand, Galton, after his classical study of mental imagery (1883), stated that scientific men, as a class, have feeble powers of visual representation. He had appealed for evidence of visual recall to distinguished scientists because he thought them more capable than others of accurately stating the results of their introspection. He had recourse not only to English but to foreign scientists, including members of the French Institute. "To my astonishment," he writes, "I found that the great majority of men of science to whom I first applied protested that mental imagery was unknown to them, and they looked on me as fanciful and fantastic in supposing that the words 'mental imagery' really expressed what I believed everybody supposed them to mean. They had no more notion of its true nature than acolor-blind man, who has not discerned his defect, has of the nature of color." One scientist confessed that it was only by a figure of speech that he could describe his recollection of a scene as a mental image to be perceived with the mind's eye.
When Galton questioned persons whom he met in general society he found "an entirely different disposition to prevail. Many men and a yet larger number of women, and many boys and girls, declared that they habitually saw mental imagery, and that it was perfectly distinct to them and full of color." The evidence of this difference between the psychology of the average distinguished scientist and the average member of general society was greatly strengthened upon cross-examination. Galton attributed the difference to the scientist's "habits of highly generalized and abstract thought, especially when the steps of reasoning are carried on by words [employed] as symbols."
It is only by the use of words as symbols that scientific thought is possible. It is through coöperation in work that mankind has imposed its will upon the creation, and coöperation could not have been carried far without the development of language as a means of communication. Were it not for the help of words we should be dependent, like the lower animals, on the fleeting images of things. We should be bound to the world of sense and not have range in the world of ideas. Words are a free medium for thought, for the very reason that they are capable of shifting their meaning and taking on greater extension or intension. For example, we may say that the apple falls because it is heavy, or we may substitute synonymousphraseology that helps us to view the falling apple in its universal aspects. The mind acquires through language a field of activity independent of the objective world. We have seen in an earlier chapter that geometry developed as a science is becoming gradually weaned from the art of surveying. Triangles and rectangles cease to suggest meadows, or vineyards, or any definite imagery of that sort, and are discussed in their abstract relationship. Science demands the conceptual rather than the merely sensory. The invisible real world of atoms and corpuscles has its beginning in the reason, the word. To formulate new truths in the world of ideas is the prerogative of minds gifted with exceptional reason.
To be sure, language itself may be regarded as imagery. Some persons visualize every word spoken as though it were seen on the printed page; others cannot recall a literary passage without motor imagery of the speech organs or even incipient speech; while others again experience motor imagery of the writing hand. With many, in all forms of word-consciousness, the auditory image is predominant. In the sense of being accompanied by imagery all thinking is imaginative. But it is the use of words that permits us to escape most completely from the more primitive forms of intelligence. So directly does the printed word convey its meaning to the trained mind that to regard it as so much black on white rather than as a symbol is a rare and rather upsetting mental experience. Words differ among themselves in their power to suggest images of the thing symbolized. The word "existence" is less image-producing than "flower," and "flower" than "redrose." It is characteristic of the language of science to substitute the abstract or general expression for the concrete and picturesque.
When, therefore, we are told that the imagination has been at the bottom of all great scientific discoveries, that the discovery of law is the peculiar function of the creative imagination, and that all great scientists have, in a certain sense, been great artists, we are confronted with a paradox. In what department of thought is imagination more strictly subordinated than in science? Genetic psychology attempts to trace the development of mind as a means of adjustment. It examines the instincts that serve so wonderfully the survival of various species of insects. It studies the more easily modified instinct of birds, and notes their ability to make intelligent choice on the basis of experience. Does the bird's ability to recognize imply the possession of memory, or imagery? Increased intelligence assures perpetuation of other species in novel and unforeseen conditions. The more tenacious the memory, the richer the supply of images, the greater the powers of adaptation and survival. We know something concerning the motor memory of rodents and horses, and its biological value. The child inherits less definitely organized instincts, but greater plasticity, than the lower animals. Its mental life is a chaos of images. It is the work of education to discipline as well as to nourish the senses, to teach form as well as color, to impart the clarifying sense of number, weight, and measurement, to help distinguish between the dream and the reality, to teach language, the treasure-house of our traditional wisdom, and logic, so closely related to the right use oflanguage. The facts of abnormal, as well as those of animal and child psychology, prove that the subordination of the imagination and fancy to reason and understanding is an essential factor in intellectual development.
No one, of course, will claim that the mental activity of the scientific discoverer is wholly unlike that of any other class of man; but it leads only to confusion to seek to identify processes so unlike as scientific generalization and artistic production. The artist's purpose is the conveyance of a mood. The author ofMacbethemploys every device to impart to the auditor the sense of blood-guiltiness; every lurid scene, every somber phrase, serves to enhance the sentiment. A certain picture by Dürer, a certain poem of Browning's, convey in every detail the feeling of dauntless resolution. Again, a landscape painter, recognizing that his satisfaction in a certain scene depends upon a stretch of blue water with a yellow strand and old-gold foliage, proceeds to rearrange nature for the benefit of the mood he desires to enliven and perpetuate. It is surely a far cry from the attitude of these artists manipulating impressions in order to impart to others an individual mood, to that of the scientific discoverer formulating a law valid for all intellects.
In the psychology of the present day there is much that is reminiscent of the biological psychology of Aristotle. From the primitive or nutrient soul which has to do with the vital functions of growth and reproduction, is developed the sentient soul, concerned with movement and sensibility. Finally emerges the intellectual and reasoning soul. These three partsare not mutually exclusive, but the lower foreshadow the higher and are subsumed in it. Aristotle, however, interpreted the lower by the higher and not vice versa. It is no compliment to the scientific discoverer to say that his loftiest intellectual achievement is closely akin to fiction, or is the result of a mere brooding on facts, or is accompanied by emotional excitement, or is the work of blind instinct.
It will be found that scientific discovery, while predominantly an intellectual process, varies with the nature of the phenomena of the different sciences and the individual mental differences of the discoverers. As stated at the outset the psychology of scientific discovery must be the subject of prolonged investigation, but some data are already available. One great mathematician, Poincaré, attributes his discoveries to intuition. The essential idea comes with a sense of illumination. It is characterized by suddenness, conciseness, and immediate certainty. It may come unheralded, as he is crossing the street, walking on the cliffs, or stepping into a carriage. There may have intervened a considerable period of time free from conscious effort on the special question involved in the discovery. Poincaré is inclined to account for these sudden solutions of theoretical difficulties on the assumption of long periods of previous unconscious work.
There are many such records from men of genius. At the moment the inventor obtains the solution of his problem his mind may seem to be least engaged with it. The long-sought-for idea comes like an inspiration, something freely imparted rather than voluntarily acquired. No mental process is moreworthy to command respect; but it may not lie beyond the possibility of explanation. Like ethical insight, or spiritual illumination, the scientific idea comes to those who have striven for it. The door may open after we have ceased to knock, or the response come when we have forgotten that we sent in a call; but the discovery comes only after conscious work. The whole history of science shows that it is to the worker that the inspiration comes, and that new ideas develop from old ideas.
It may detract still further from the mysteriousness of the discovery-process to add that the illuminating idea may come in the midst of conscious work, and that then also it may appear as a sudden gift rather than the legitimate outcome of mental effort. The spontaneity of wit may afford another clue to the mystery of scientific discovery. The utterer of a witticism is frequently as much surprised by it as the auditors, probably because the idea comes as verbal imagery, and the full realization of their significance is grasped only with the actual utterance of the words. The fact that to the scientific discoverer the solution of his problem arrives at the moment when it is least sought is analogous to the common experience that the effort to recall a name may inhibit the natural association.
The tendency to emphasize unduly the rôle played by the scientific imagination springs probably from the misconception that the imagination is a psychological superfluity, one of the luxuries of the mental life, which should not be withheld from those who deserve the best. The view lingers with regard to the æsthetic imagination. James could not understand the biological function of the æsthetic faculty. On the alleged uselessness of this phase of the human mind A. J. Balfour has recently based an argument for the immortality of the soul. This view is strikingly at variance with that which inclines to identify it with that mental process which creates scientific theories and thus paves the way for the adjustment of posterity to earthly conditions.