a voltage of only about 13 volts, while about 80 volts Physical Laboratory, University of X-Ray Fluorescence and the Quantum Theory. THE experimental conclusions which I briefly outlined in a letter to NATURE of February 18 point directly to a theory of X-ray fluorescence and of the emission of radiation in quanta, which certainly bears a resemblance to Bohr's theory of line spectra. The experimental evidence obtained is, however, so direct that there seems little possibility of escape from the conclusions given below. Indeed, the theory was forced upon the writer directly by the experimental results, and it was only afterwards that he was reminded of some similarity with the theory of Bohr based on the Rutherford atom. It is an experimental fact that in the case carefully investigated (and obviously in many, if not in all, other cases), the ejection from an atom of an electron associated with a fluorescent X-radiation of frequency n necessitates an absorption of energy greater than the kinetic energy carried away by the electron by approximately the energy (hn) of one quantum of radiation of frequency n. Thus : (1) Total absorption per electron emitted=mv2 + hn (approximately) that is, the energy required to separate the electron (a K electron, say) from the parent atom, is approximately equal to the energy of a quantum of the fluorescent radiation of series K associated with that electron. The energy of a quantum of radiation may therefore be regarded as the mutual potential energy of the separated atom and electron, measured from the zero given by the electron in its normal position and state. When the displaced or any other electron falls back into the position of the displaced electron, the energy is re-emitted as a radiation characteristic of the atom, and this, of course, in definite quantity. So much may be claimed as at any rate giving a first approximation to the truth. The results of experiments, however, suggest the possibility of the necessity for some modification of this theory in detail, though not in principle. For in the one case thoroughly investigated we get a nearer approximation to the experimental results by writing (2) Total absorption per electron emitted = {mv2 + hng+hn, where ng and n1 are the frequencies of the K and L fluorescent radiations respectively. As the third term (hn.) is at its maximum value only about 7 per cent. of the whole, it is impossible at this stage to say definitely whether or not it expresses a physical fact. This term was, however, suggested by a consideration of the probable process following the ejection of a K electron. The relation indicates that possibly the energy required to free a K electron is equal to the sum of the energies of quanta of K, L, and any other fluorescent radiation of lower series M, N. etc.-presumably originating in vibrations in the outer rings of the atom. If we accept this provisionally it means that the energy of a quantum of K radiation is that required to displace a K electron into the position of an L electron, while the energy of a quantum of L radiation is that required to displace an L electron into the position of an M electron, and so on. Such a process may never occur; it is, however, a convenient way of expressing the energy required completely to eject the electron in terms of steps which can only be regarded as extremely probable in the inverse process involving radiation. Thus the energy of a quantum of K radiation is left in the atom from which a K electron is hurled; or possibly the energies of one quantum of each of the fluorescent radiations, K, L, M, etc., are left in the atom. This energy must, of course, be radiated while the atom is regaining its original configuration by the absorption of an electron into the K position. It seems probable, however, that the readjustment of the atom and the principal radiation take place even before the atom as a whole regains an electron, by an L electron falling into the position of a displaced K electron, an M electron replacing an L electron, and so on; only the final stage of the readjustment being completed by the absorption of an electron into an outer depleted ring. It is obvious in this case-unlike that studied by Bohr-when and why an electron falls into an inner ring; it is simply subsequent to and due to the removal of an inner ring electron. No new principle of radiation is involved, yet it accounts for radiation taking place in quanta. We should thus expect L radiation to be associated with the emission of K electrons as well as with L electrons. Search for such a radiation is at present being made. Pointing to the probability of such an associated radiation is the fact that when hn, becomes a smaller fraction of the whole absorption, the discrepancy found when it is omitted, as in equation (1), diminishes. Not only is this so, but the energy of the corpuscular radiation and of the K fluorescent radiation actually emitted, do not quite fully account for the whole energy absorbed. The discovery of the L radiation in calculated intensity would give almost perfect agreement. In spite of these indications the writer hesitates to make a definite statement about the physical reality of the third term concerned with L radiation; experiments will very soon decide the point. In either case we have the direct evidence that the energy of a quantum is simply energy absorbed in removing the corresponding electron from its normal orbit; it is the energy afterwards set free, presumably when the electron returns. It is hoped that experiments now being undertaken will determine also if X-ray fluorescence-that arising from the vibration of inner ring electrons can be appreciably delayed by retarding the return of the ejected or other electrons from outside the atom. It is more probable that X-ray phosphorescence will not be detected, the readjustment of the interior of the atom taking place immediately after the ejection of an inner electron, and the final absorption of an electron into a surface ring being the only part of the process susceptible to external conditions. The subject can, however, only receive adequate treatment in communications to other journals. C. G. BARKLA. University of Edinburgh, February 27. The Physical Properties of Isotopes. PROF. SODDY's letter in NATURE of February 4 would seem to lead to certain interesting conclusions about the structure of the atom. It is easy to show that two elements of different atomic weight must differ either in their chemical or in their physical properties. If elements are inseparable chemically their affinity A тат dT if T is the tem must be equal. Now A=-T The fact that emerges most clearly from all the work done on this subject is that the atomic heats of similar substances may all be represented by the same function f(v) of the atomic frequency v. Therefore, if A is the same for isotopes, and this would seem to be the definition of the word, their atomic frequencies must be identical. But as v is a function of the atomic weight and of the forces acting between the atoms, the latter must vary when the atomic weights are different. If the force of attraction between two atoms is ap(r) and the repulsive force by(r), r being the distance, then at a sufficiently low temperature the quasi-elastic force holding an atom in position is 2k(ap'(r) – by' (r)). The constant k represents the action of the surrounding atoms and depends only upon the type of space-lattice formed by the atoms. As the atomic frequency V= is the same for all ad (n) -bh() a = M 2π a M isotopes, atomic weight M may be. As Prof. Soddy has shown that the atomic volume and consequently is also constant, it follows that both a and b must be proportional to the atomic weight. must be identical, whatever the This conclusion might, perhaps, be tested by a measurement of the vapour pressure of the different sorts of lead. The latent heat of sublimation A is prothat is to M, as ris proportional to a sp(r)dr – bfy(r)dr, v cannot vary, and as Prof. Soddy has shown that r is constant, the melting point Tm should be proportional to M. Thus, for instance, the melting point of Prof. Soddy's lead should be 1.54° higher than that of ordinary lead. In all probability the atomic weight of the final product of thorium is 2084, in which case the difference in the melting point should be as much as 3:75. These consequences are not necessary but, admitting the absolute chemical identity, highly probable. They include the assumption that the radii of the atoms are equal as well as their mean distance apart in the solid state. In any case, a measurement would seem well worth while, as a negative result would be of almost as great interest as if a difference were observed. Unfortunately, the elastic constants which should vary by a corresponding amount can scarcely be measured with sufficient accuracy. The following conclusions about the structure of the atom would seem to result. The purely chemical properties are determined by the external electrons which probably also account for the apparent radius of the atom. The forces of attraction and repulsion between the atoms, the interaction of which results in the solid state, have their origin in the nucleus. In isotopes they are proportional to the atomic weight, i.e. probably to the number of positive particles. They cannot, however, be considered simply as the sum of the forces between the positive particles, as they are additive only in isotopes, that is, when the charge on the nucleus is equal. The simplest assumption, therefore, would appear to be that the nuclei of isotopes differ in their linear dimensions, but not at all, or only very little, in the arrangement of the particles. F. A. LINDEMANN. Sidholme, Sidmouth, February 10. The Green Flash. PROF. PORTER'S explanation of the green flash (NATURE, February 18) is unable to account for its appearance at sunrise, when it can be observed with great brilliance. When I was passing through the Indian Ocean on my way to observe the total eclipse of 1875 I happened to be on deck before sunrise one morning, and, watching for the first ray of the sun, was surprised to see the first flash of light appear as a vivid green. I had never heard of the phenomenon before, but atmospheric dispersion seemed to me sufficient to account for it, and I took it for granted that it was a well-known occurrence. I continued to observe the same effect several mornings in succession. Since then I have undertaken many sea journeys, and though I do not recollect having ever again observed the flash or tried to observe it at sunrise, I have never lost an opportunity of watching for it at sunset. My experience does not support Prof. Porter's explanation, because the redder the sun at sunset, the less likely is the green flash to appear. The atmospheric conditions must be such that there is as little absorption as possible of the more refrangible part of the spectrum. Those who want to see the appearance at its best should keep one eye closed as long as possible, and when the sun is just about to disappear, shut the eye which has been watching the setting sun, and open the other, which is then unaffected by the troublesome after-images which are otherwise seen. It is, of course, impossible to open the eye just at the critical moment, so that this alone is not sufficient to disprove Prof. Porter's explanation. ARTHUR SCHUSTER. Yeldall, Twyford, Berks., February 21. Hormones and Heredity. I THE reviewer of Mr. H. Elliot's translation of Lamarck's Philosophie Zoologique" in NATURE of February 11 remarks: "Unless we have misunderstood, a similar suggestion was made by Mr. J. T. Cunningham in 1908." The word "similar refers to an alleged suggestion by Prof. MacBride that hormones may afford a clue to a possible modus operandi of the transmission of modifications. should be glad to know when and where Prof. MacBride's suggestion was published, as I have not heard of it before. It would seem from the terms of this review that neither Mr. H. Elliot nor J. A. T. are fully acquainted with my paper on the heredity of secondary sexual characters in relation to hormones, published in the Archiv für Entwicklungsmechanik in 1908. The hormone theory of heredity is elaborated in considerable detail in my paper. I do not think it is possible to misunderstand it, and it is much more than a "suggestion." J. T. CUNNINGHAM. S.W. Polytechnic, Chelsea. February 15. It seemed to me that there was some historical interest in recalling Mr. Cunningham's paper of 1908. 64 Το As I was unable at the time to refresh my memory on the subject, I wrote guardedly, "Unless we have misunderstood." A fitter expression would have been, "If we remember aright." It is satisfactory to know that my recollection was substantially correct. object to the theory being called a suggestion" seems fastidious. As to Prof. MacBride's suggestion, Mr. Elliot's reference was to a proof of vol. i. of "A Treatise on Embryology." J. A. T. THE NATURAL HISTORY BUILDING OF THE UNITED STATES NATIONAL MUSEUM.1 MR. RATHBUN has done well to publish a full technical account of this building, which claims "to be greatly in advance of all and, by giving exceptional width to the main mass, the floor area is large in proportion to the extent of outer wall. The plan, which covers nearly four acres, shows a large pavilion surmounted by a rotunda facing south, and from it three wings extending towards the east, west, and north; the latter are connected near their outer ends by two L-shaped ranges, completing the enclosure of two large uncovered courts. The length of the southern façade, shown in perspective in our Fig. 1, is 561 ft.; the greatest north and south measurement, which is along the middle block, is about 364 ft.; each court is 128 ft. square. The wings have a width of 116 ft.; and the L-shaped ranges a width of 61 ft. FIG. 1.-United States National Museum, Natural History Building, viewed from S. E., showing the South front, the outer end of the East wing, and the beginning of the East range. other museum buildings intended for a similar purpose." The three objects aimed at have been storage, usable exhibition space, and laboratory accommodation. The epithet "usable" is important, for in exhibition galleries dark corners and obtrusive architectural details are worse than useless. "Usable" also implies facility of accommodation to growing and changing needs. With this in view, the building has been planned as a great shell, with few permanent division walls; 1 " A Descriptive Account of the Building recently Erected for the Depart ments of Natural History of the United States National Museum." By Richard Rathbun. U.S. National Museum, Bull. 80. Pp. 132+xxxiv plates. (Washington, 1913.) This great width and the fact that the building is four storeys high might lead one to expect a deficiency of light. The modern classic style, however, has permitted exceptionally large windows (Fig. 1) in all but the upper storey, where, of course, skylights are available. Moreover, in these windows a maximum of glass surface has been secured by the use of light metal framing. Light is also furnished to the wings by light-wells 50 ft. wide, which break through the upper storeys and light all except the basement or ground storey. The floor of the first storey is thus all available, but the top-lit area is usually separated by glazed screens from the surrounding aisles. Our second figure shows part of an L-shaped range on this floor, with the outer windows on the right, and on the left windows to the open court. The actual interior width is 54 ft. 2 in., and the ceiling height is 20 ft. The severity of the interior is not unpleasing, and for exhibition galleries is better than any ornament. The general absence of interior structural walls has necessitated the introduction of piers and columns arranged in one or more rows, as shown on the right of our Fig. 2. These, as well as the wall piers, are at a distance of 18 ft. 6 in. from centre to centre. Rooms can be formed in hands of the workmen, but that the staff will be left to work in peace. The vacuum-cleaning pipes lead from a single pump in the basement, driven by a 25-h.p. motor, and are connected with seventy-three inlets to which can be attached rubber dust-hose provided with a complete equipment of dusting tools. These will be of particular value in the cleaning of exhibition cases. The rounds of the night-watch are controlled by a system of recording clocks with paper dials, which mark the signals and transmit them to a central station. Time is indicated by sixteen dials electrically controlled by a master clock FIG. 2.-United States National Museum, Natural History Building. The Gallery of Ethnology, on the first storey of the East range. multiples of this unit by the building of partitions between the columns, or to meet varying needs the exhibition galleries can likewise be broken up by slighter screens of material appropriate to each case. As the museum grows and changes there will be no difficulty in making such alterations, for all the mains from the heating and lighting plant run in tunnels under the basement, and are connected with each floor by two vertical chases cut in each wall pier. These chases also serve for electrical communications, ventilating flues, vacuum-cleaning pipes, hot and cold water supply, and the like. Thus for the future we can almost imagine that in this building "neither hammer, nor axe, nor any tool of iron " will be heard in the and corrected each noon from the Naval Observatory. There are six electric Otis elevators, four for passengers and two for freight. The latter are near the large wagon entrances, and run from ground to attic; their cars measure 7 ft. 3 in. by II ft. 4 in., by 12 ft. high, and can take a load of 12,000 lb. Nearly all the ground storey of the east wing is occupied by the machinery plant, which serves the older buildings also. Except for the generator engines, the two stoker engines, and six pumps in the engine-room, which are worked by steam, all motive power is supplied by electricity and is conveyed to the various laboratories and workshops. The latter consist of painters', cabinet-makers', joiners', and metal-workers' shops, all on the south of this wing. This concentration warrants the use of machinery, and almost every kind of wood-working tool, down to the oil-stone, has its individual electric motor. The "sweat of man's brow" sounds archaic here, but none the less the artisans have a shower-bath and dressing-room. Each department has also its own laboratories, work-rooms, and "comfort-rooms." The abundant storage space is fitted with standardised shelves, drawers, and cases, permitting ready rearrangement and interchange. The auditorium is well designed, accessible, and isolated. There are also two rooms for committees and small scientific meetings. This book does not profess to describe the installation of the exhibits, though a few plates (see Fig. 2) show the general effect. Its value lies in its account of structural detail and practical fitments; it should be read by every museum governor, and digested by every architect of future museum buildings. The claim advanced may not be substantiated at every point, but as regards those here mentioned it is enough to say that the United States Museum possesses what our own Natural History Museum notoriously lacks. at the hands of the excise authorities (see Nature, February 11 and 18), who imposed a duty on the spirit in which specimens coming from abroad were preserved. "Red tape seems almost too soft a material for binding the cast iron regulations which govern the Excise Department. If, however, the above principle is recognised and conceded, surely it might be adopted in a broad and, if possible, scientific spirit on the part of the authorities. It is not only carried out in the narrowest spirit of officialdom, but also is applied with an extraordinary absence of logic, such as is only conceivable where ignorance of the elements of organic chemistry exists. For example, chloroform and ether made from ethyl alcohol pay duty, whereas that from methylated spirit (methylated ether) in one case and acetone in the other do not, although the products are practically identical. Again, methyl and ethyl alcohol used for research are exempt from duty, whereas ethyl acetate and butyrate, ethyl chloride, bromide, iodide, and chloral hydrate, in all of which ethyl alcohol is used, are not exempt. The corresponding methyl derivatives. which are obtained in precisely the same way from methyl alcohol are not scheduled and, we presume, are free to all consumers. It may be seen from the table of excise regulations that chemists DUTY-FREE ALCOHOL FOR SCIENTIFIC keeping or using stills are subject to a tax of IN PURPOSES. ten shillings on each still, although it should be N the recent discussions on the best means of developing the colour industry in this country, reference has frequently been made to the duty charged upon pure methyl and ethyl alcohol, which are essential for certain products. Although the past and present stagnation is mainly due to other and much more deep-seated causes, the fact that the trade is still handicapped by a form of taxa-couraged. tion which does not exist in Continental countries is one of the signs of the steady indifference of the Government to scientific industrial development of which Thomas Thomson so bitterly complained in his history of chemistry written nearly a century ago. As the result of a very widespread feeling of dissatisfaction with the high cost of these alcohols (a feeling which had long existed in all the important centres of chemical research in this country) the subject was brought before the chemical section of the British Association at the Glasgow meeting in 1901, and an influential committee was formed, which was successful in persuading the Board of Inland Revenue to forgo the duty on methyl and ethyl alcohol used for scientific purposes in approved institutions. Their recommendations were embodied in the Finance Act of 1902, the working of which has, we believe, given general satisfaction. Whether or not the laboratories of manufacturing firms are permitted to share these advantages we cannot state. Yet in spite of the virtual, if tardy, concession of the principle that research can be usefully promoted in this way, one is constantly confronted with the sort of trivial annoyance such as Sir William Ramsay and Prof. Hickson have recently suffered But it is not the duty on alcohol which has been the main factor in crippling the colour industry during the last thirty years. Nor is it defective training, equipment, or ability of the young chemists turned out from our universities, whose scientific work stands second to none. It is that the manufacturing world is only beginning to realise at this time of crisis in the chemical industry the true value of the research chemist. We say "beginning to realise," for it was only a few. days ago that a professor of chemistry in one of our provincial universities received a request from a large and wealthy corporation to recommend a first-rate chemist, to whom the handsome salary of thirty shillings a week was offered, or about a third of the earnings of a coal-miner working full time! It would take up too much space to attempt to trace the cause of that attitude of indifference among nearly all classes to the application of scientific research to industry which is such a striking feature of German commercial development. There can be no question that the key to the problem is to be found in our educational system. The very terms "humanities" and "stinks" are fraught with deep significance. They would appear to contrast what is real and living |