Popular Science Monthly/Volume 84/June 1914/The Progress of Science
RUTHERFORD ON THE CONSTITUTION OF MATTER
The most notable features of the annual meeting of the National Academy of Sciences held, in Washington in the third week of April were two lectures by Sir Ernest Rutherford, the distinguished physicist of the University of Manchester. These are the first of a series of lectures, established by the children of William Ellery Hale, which are to treat problems of evolution from the atom to man. At the autumn meeting of the academy, stellar evolution will be reviewed by Dr. W. W. Campbell, director of the Lick Observatory. Sir Ernest's lectures, which were reported stenographically, will be printed in Science and ultimately in a book with the other lectures of the series. It is almost impossible to represent their contents by an abstract, but in view of the great interest and importance of the subject and the originality of some of the experiments and theories, it may be well to attempt to give an outline.
Sir Ernest began by reminding his audience that the idea that matter is composed of very minute discrete particles incapable of subdivision and therefore called atoms was familiar to the Greeks, atom in their language being equivalent to the indivisible. This idea was little developed until the beginning of the last century when Dalton first applied it to the chemical constitution of compounds showing that each separate element such as oxygen, iron, nitrogen, etc., always combines in a certain definite equivalent proportion. This is in fact the basal conception of modern chemistry and renders it possible to derive the composition of a substance from a chemical analysis. Chemistry thus lent exceedingly strong support to the hypothesis of the atomic constitution of matter, but no further advance in the subject was made till about the middle of the century when the so-called kinetic theory of gases was developed by Clausius and Maxwell. This theory accounts for the pressure and other properties of gases by supposing them constituted of single atoms, or of small groups of atoms united into molecules, moving with an amount of energy which is proportional to the temperature. The mathematical developments of this theory and the conclusions to be drawn from the formulas have been verified in cases so very numerous that no one now or for a long time has doubted the essential correctness of the underlying hypothesis. In spite of the conviction that the kinetic theory was true, it was for long supposed that no actual demonstration of atomic or molecular structure could ever be reached. Of late years, however, the study of an almost forgotten phenomenon called the Brownian movement has led to actual demonstrations. Brown as long ago as 1827 observed that microscopic spores of plants suspended in a liquid were in constant motion. The smaller the particles the more actively they were displaced while their movements were thoroughly irregular, the spores passing one another in opposite directions or intersecting one another's paths without any general drift such as would have resulted from ordinary currents in the fluids due, for example, to differences of temperature. Of late years this Brownian movement has been studied with great precision by M. Perrin and others. It has been established that particles sufficiently small, say one ten thousandth of an inch in diameter, are really displaced in a random manner by the vastly smaller invisible molecules of the fluid in which they are suspended, and that the movements of the molecules can be directly inferred from those of the Brownian particles.
Much more spectacular is the evidence afforded by the cathode rays developed in Crooke's tubes. In these tubes there is emitted from the cathode a stream of luminosity which has very remarkable properties especially that of being deflected by a magnet. This shows that the luminous ray is composed of material particles in motion and charged with electricity. Just to what extent these particles consist of ordinary matter and in how far merely of the electric charge is more or less problematical, but many physicists consider the moving entities as atoms of electricity and this also appears to be Sir Ernest Rutherford's view. These particles are now usually called electrons and they have been identified with the so-called beta rays emitted by radioactive products.
Radium results from the degeneration of uranium, though there are intermediate products, and radium itself likewise gives rise to a series of radioactive products differing from one another. In each of these cases of degeneration, the process is similar. Radium decomposes with the emission of two sorts of rays called the alpha rays and the beta rays. The alpha rays are neither more nor less than atoms of the gas helium, long since known to exist in the sum by its spectrum, and more recently detected in a uranium ore. The beta particles are identical with the electrons which form the cathode rays. The alpha particles are expelled from the radium at a tremendous velocity, but this is far exceeded by the velocity of the beta rays. Sir Ernest Rutherford and his colleagues in radiological investigation have succeeded not only in determining the identity of the alpha particles with helium, but also in establishing the relative size of the electrons and the atoms of helium. The mass of the beta particles is only about one seven-thousandth part the size of the helium atom, and most of the heating effect of radium is due to the energy of the larger alpha particles.
So far has the analysis of these products progressed, and so delicate is the apparatus devised for the study, that Rutherford and Geiger have actually succeeded in making either alpha or beta particles one by one give rise to electrical discharges and light in such a way that the number of either kind of particles emitted per second from a given mass of radioactive matter can be counted. The most efficient apparatus for this purpose is called the string electrometer, so designed as to give a record consisting of small notches on a continuous line. It is like the record of a chronograph and in fact the instrument may be considered as a chronograph. Of this record the notches produced by the alpha particles greatly exceed in depth those given by the beta particles, and thus the rate at which each is given off can be studied with the utmost accuracy on a permanent record.
In a popular description of this kind it is difficult to convey an idea of the extraordinary sensitiveness of the apparatus devised, and none at all of the genius which was requisite to its development, but perhaps enough has been said to show that the most carefully hidden secrets of the ultra-microscopic structure of matter are now subject to scrutiny, and that before long many of its features will be fairly well understood. Sir Ernest concluded his lecture by an illustration of the number of atoms contained in a cubic centimeter of helium. It was something like this. If one hundred million people were to undertake to count these atoms, each person enumerating four per second day and night, the tale would be complete in a couple of thousand years.
THE STRUCTURE OF THE ATOM
Sir Ernest Rutherford's second lecture dealt with the problems of the structure of the atom and the bearings of recent researches on this subject. The lecture was most eloquent and left the audience in a condition of the greatest enthusiasm which they testified by rising to give a hearty vote of thanks to the lecturer.
The speaker began by enumerating some of the better known properties of radium and the radioactive products, such as the rate of decay of these substances, ranging from five thousand million years for the half period of uranium down to a few minutes for some of its descendants. He mentioned also the enormous energy of radioactive disintegration, showing that one pound of a radioactive product, if one could gather so much, has the explosive energy of ten million pounds of nitroglycerin. He dwelt also upon the experimental methods developed by Mr. P. T. R. Wilson by which the expulsion of alpha particles and beta particles can be made visible and even photographed. The first part of the path of the alpha particles is nearly straight, but as they lose energy, contact with molecules of other substances deflects them in a characteristic manner. The beta particles, on account of their greatly inferior mass, pursue very irregular courses.
Less well known are the results obtained by Moseley on the interference spectra of X-rays produced by reflection from crystals, especially that of rock salt. These spectra are capable of being photographed and are vastly more simple and more regular than those obtained from visible light. These spectra evince a regularity among the elements which does not appear in the more familiar light spectra, and these regularities tend to elucidate the nature of the atom.
Lord Kelvin conceived an atom as composed of negative electrons included within a space charged with positive electricity holding the electrons together in a single body. This, however, appears to be inconsistent with the researches of Rutherford, who has developed a theory of nuclear atoms, according to which a central nucleus of extremely high potential is surrounded by negative electrons whose motion it controls. If so, the electrons are controlled by the nucleus very much as the planets are held to the solar system by gravitation, and indeed there appears strong reason to suppose that the force involved is really inversely proportional to the square of the distance as in the case of gravitation. From this point of view, the various elements are characterized by the number of electrons in the atom. Each electron carries a single negative charge, and the nucleus carries as many positive charges as there are electrons to be controlled. This theory of the atomic constitution explains the irregularity in the movement of alpha particles through a gas. When an alpha particle approaches a nucleus carrying a charge of millions of volts, it is sharply deflected and may appear even to rebound in the direction from which it came. Sir Ernest illustrated this by a fine experiment. Similarly, if there were a small hole drilled through the center of the earth, a ball dropped from the surface would go straight down and come straight back almost as if it had been infinitely elastic and rebounded from an impenetrable surface.
It isto determine the number of positive charges contained in each one of the elements from hydrogen to uranium, and it seems also that if the elements are appropriately arranged the charges increase by unit steps, so that hydrogen contains a single positive charge and uranium 92. This assumption corresponds to the actual elements with a small but very important exception. In the series of 92 possible charges, there are just three gaps, corresponding, presumably, to three unknown elements, and at the same time the relationship of these unknown elements to the known elements is made clear, so that the chemists have preliminary information to guide them in the search for the missing links. This is a wonderful advance on the periodic system of Mendelèef which has itself been fruitful in the discovery of elements.
THE SMALL COLLEGE AND ITS PRESIDENT
The writer of the article on "The Small College and its President" which appealed in the May number of
The Popular Science Monthly writes to the editor to the effect that certain college teachers have professed to be able to find a personal application in the article in question. It has been charged that the picture of "our college" represents a certain trans- institution, and that, concealed in the article, are various allusions to particular persons connected therewith. In order to correct this very serious misconception, the writer desires to make the following statement:
The institution referred to as "our college" is purely imaginary, or to speak more correctly, it is a composite picture intended to represent the typical American small college. It is doubtless true that the adherents of any particular college can find in the description details which fit their institution. Were this not the case the article would fail of its purpose as a composite portrait of all the colleges; but it will be found impossible to fit the entire description to any particular college, and it certainly was no particular college that the writer had in mind.
In his description of the size of the college, its faculty, the town in which it is located, its buildings, etc., the writer spoke entirely at random, and tried to picture what may fairly be regarded as average conditions. Since the resulting criticism has been brought to his attention, he has tried to fit the description to a particular college, but without success. He finds, however, that there are some three or four middle-west colleges which, if dismembered and patched together again in the proper pattern might make an institution which would fit pretty well for "our college." The description of the conditions in "our college" are, he believes, typical of the American small college, taking the best with the worst and averaging them, and he has arrived at this conclusion after wide reading in which the valuable reports of the Carnegie Foundation have not been neglected. The reference to the innocuous professor whose beautiful character compensated for the absence of scholarship was intended to represent a not unfamiliar type (at least in some of the older colleges) though the writer will plead guilty to being strongly reminded, while writing it, of the former incumbent of the chair of Latin in a certain eastern college. The incident of the professor who was criticized by one of the trustees for "inefficiency" because he staid at home and attended to his business, was related to the writer about ten years ago, and concerns a college which, so far as he is concerned, shall remain nameless. Suffice it to say that, so far as he has yet learned, nobody has suspected that the article refers in any way to that particular college. The writer does not even know the names of the principals in the case. These few instances will indicate the imaginary and composite character of "our college." It was represented as being on the Carnegie Foundation lest the foundation colleges, reading the article, point their finger at the outside institutions and say: "This is intended for you!" The evils incident to what the writer regards as a defective system of college organization affect the foundation colleges equally with the others, though the standard of the foundation colleges of course averages much higher. In fact these evils are not unknown in the universities, but there the problem is much complicated by other factors, and should for that reason be separately considered.
Least of all was it the intention to utter any criticism either on the president or trustees of the small college. The description of the president of "our college" is not a portrait, and the same is true of the trustees. Trustees, president and faculty, are alike victims of what the writer believes to be a defective system, and of the three the president is perhaps most to be pitied. Too i often does he find himself in the position of being ground between the upper and the nether millstone. The trustees, as the writer knows them in more than one college, are high-minded, disinterested men, serving without recompense and often with a high degree of self-sacrifice. If anything was made clear in the article in question it was this: that any criticism either of president or trustees was directed not at individuals but at a system which demands impossible tasks of both.
We regret to record the deaths of Dr. , distinguished for his contributions to mathematical astronomy; of Dr. Charles Santiago Sanders Peirce, known for his work in logic and mathematics; of Professor , formerly state geologist of Minnesota, and of Professor , the eminent Austrian geologist.
Dr. , of Philadelphia, has been elected president of the Fifth International Congress of Surgeons to be held in Paris in 1917.—The Willard Gibbs medal of the Chicago section of the American Chemical Society has been presented to Dr. Ira Remsen, of the Johns Hopkins University.—Former students of Professor John Henry Comstock have raised a fund, to be known as the Comstock Memorial Library Fund, which is to be presented to Cornell University for a permanent memorial of Professor Comstock's forty years of distinguished service as instructor and professor of entomology.
The National Academy of Sciences at its annual meeting on April 22 presented its "medals for eminence in the application of science to the public welfare," to Colonel George Washington Goethals and Brigadier General William Crawford Gorgas. The presentation was made by Dr. William H. Welch, president of the academy, at a dinner held in honor of the retiring president. Dr. Ira Remsen, and the retiring home secretary. Dr. Arnold Hague.
Members of the National Academy of Sciences were elected at the annual meeting as follows: Ernest Merritt, physicist, Cornell University; Moses Gomberg, chemist, University of Michigan; Edward Curtis Franklin, chemist, Stanford University; Frederick Leslie Ransome, geologist, U. S. Geological Survey; ; botanist, New York Botanical Garden; Henry Herbert Donaldson, neurologist, Wistar Institute of Anatomy; , zoologist. The Johns Hopkins University; Francis Gano Benedict, chemist, nutrition laboratory of the Carnegie Institution; , physiologist, Harvard University; , ethnologist, Bureau of American Ethnology.
At its annual meeting in Philadelphia the American Philosophical Society elected to membership the following residents of the United States: , Washington; James Wilson Bright, Baltimore; , Philadelphia; Thomas McCrae, Philadelphia; , New York; , Washington; Samuel Jones Meltzer, New York; , Berkeley; , Chicago; , Urbana; , Princeton; , Philadelphia; Palmer Chamberlaine Ricketts, Troy; Harold A. Wilson, Houston; Frederick Eugene Wright, Washington. Foreign residents were elected as follows: Shibasaburo Kitasato, Tokyo; Heike Kamerlingh Onnes, Leyden; Vito Volterra, Rome.