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 Bleriot aeroplane said: "The Bleriot IV in the form of a bird ... does not appear to give good results, perhaps on account of the lack of stability, and Bleriot, 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 Bleriot 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, Bleriot crossed the English Channel in his monoplane, all the world knew that man"s conquest of the air was a _fait accompli_.
About three years after Langley"s death the Board of Regents of the Smithsonian Inst.i.tution 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 Inst.i.tution, 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 LANGLEY 1834-1906
SECRETARY OF THE SMITHSONIAN INSt.i.tUTION 1887-1906
DISCOVERED THE RELATIONS OF SPEED AND ANGLE OF INCLINATION TO THE LIFTING POWER OF SURFACES WHEN MOVING 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.
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."
REFERENCES
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 (ill.u.s.trated).
_Langley Memoir on Mechanical Flight, Smithsonian Contributions to Knowledge_, vol. 27, no. 3 (ill.u.s.trated).
_Scientific American_, Jan. 13, 1912, A Memorial Honor to a Pioneer Inventor.
_The Smithsonian Inst.i.tution 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 Inst.i.tution, 1914 (ill.u.s.trated).
CHAPTER XVIII
SCIENTIFIC HYPOTHESIS--RADIOACTIVE SUBSTANCES
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 (?p??es??, 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 role in experimental science 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 (?????, sun), an element previously revealed by spectrum a.n.a.lysis as a const.i.tuent of the sun. In the same year Rontgen, 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 a.s.sociated with phosph.o.r.escence, tested the photographic effects of a number of phosph.o.r.escent substances. He exposed, among other compounds, crystals of the double sulphate of uranium and pota.s.sium to sunlight and then placed upon the crystals a photographic plate wrapped in two thicknesses of heavy black paper. The outline of the phosph.o.r.escent 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 phosph.o.r.escent salts. To his surprise he obtained a clear image when the plate was developed. He now a.s.sumed the existence of invisible rays similar to X-rays. They proved capable of pa.s.sing 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-phosph.o.r.escent. Becquerel"s original hypothesis was thus overthrown.
Radiation is a property inherent in uranium and independent both of light and of phosph.o.r.escence.
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 a.s.sumption 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 a.n.a.lysis of pitchblende made by Mme. Curie (a.s.sisted by M.
Curie) polonium was found a.s.sociated with bis.m.u.th. Radium, also discovered in this a.n.a.lysis of 1898, was a.s.sociated with barium. Mme.
Curie succeeded in obtaining the pure chloride of radium 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 ma.s.s. 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 a.s.sociated with them were influenced by the hypothesis that radioactivity is an _atomic property_ of 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 prominent workers 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 a particles (atoms of helium minus two negative electrons), particles, or electrons (charges of negative electricity), and ? rays, of the nature of Rontgen 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 ? rays, with velocity sufficient to penetrate two feet of lead. It is through these radiations that spontaneous transformation takes 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 ma.s.s of a 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 a.s.sumption 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.
_List of Radioactive Substances_
URANIUM a particles Uranium X + ?
Uranium Y IONIUM a
RADIUM a + slow Emanation a Radium A a Radium B + ?
Radium C { C{1} a + + ?
{ C{2} RADIUM D } RADIO-LEAD } slow Radium E + ?
Radium F } Polonium } a
THORIUM a MESOTHORIUM 1 no rays Mesothorium 2 + ?
RADIOTHORIUM a Thorium X a + Emanation a Thorium A a Thorium B slow Thorium C { C{1} a { C{2} a Thorium D + ?
ACTINIUM no rays Radio-actinium a + Actinium X a Emanation a Actinium A a Actinium B slow Actinium C a Actinium D a + ?
Even a glance at this long list of new elements reveals certain a.n.a.logies between one series of transformations and another. Each series contains an emanation, or gas, which through the loss of a 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 a.n.a.logies.
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 trans.m.u.tations 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 trans.m.u.ting the metals, but of acting _as 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 bis.m.u.th 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, a.s.sumed that atoms are far different from the ma.s.sy, hard, impenetrable particles that Newton took for granted, Sir J.
J. Thomson and his school were studying the const.i.tution 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 a.s.sumes that the greater ma.s.s 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 a.s.sumption 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 antic.i.p.ate 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 a.s.sumption, 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 a.s.sumption plays a large part in our mental att.i.tude toward practical affairs should make us wary of contesting the legitimacy of scientific hypotheses.