Isaac was not the almost superhuman moral paragon which for long it was the fashion to suppose him; he had a petulant dislike of opposition, a tendency to keep his discoveries to himself instead of letting the world have the benefit of them -in which he compares badly with the frankness of Leibniz-and a rather mean revengefulness, as in his treatment of Flamsteed, whose observations had been pre-eminently useful to him. On the other hand, De Morgan readily acclaims him as the greatest scientific genius of all time, and indeed above the average level of his time as to character also. His protest is merely against excessive veneration. Section viii. of the last essay is on Newton's religion, which has been the subject of much debate. The Unitarians claim him, and, in spite of Brewster, they are probably right. There is a small mistake in the footnote on p. 21-"Uranus" should be "Neptune "--but we mention it only in order that it may be put right in the next edition. We see no other slips, and the editor is to be congratulated on a piece of good work. (3) This book is not so much a new edition of the English translation of Prof. Mach's "Contributions to the Analysis of the Sensations," published in 1897, as an entirely new work; for it is considerably enlarged. Its contentions, however, are the same, and the expansion is in the details. Mach disclaims the title of philosopher, considering himself a physicist; but inasmuch as he seeks a unifying principle applicable to all sciences, he philosophises. According to his view, all experience is made up of elements which are best regarded as of one kind. The distinction of material and psychical, of subject and object, is mischievous. All experience is of one stuff, and the task of science is to investigate relations. psychical fact is as real as a material fact; indeed, each element exists in both the worlds, according to our purposes of the moment. And as this web of experience and its threads of relations-is all that we need concern ourselves with, we can throw overboard the Dinge an sich which modern philosophy inherits from Kant, and with these useless noumena lying behind material phenomena we can throw overboard the noumenon which lies or was supposed to lie behind our own mental phenomena. Α This radical abolishment of the ego is the main difficulty. Mach counters the inevitable question "Who experiences?" by saying that the question itself shows the questioner to be still in the bonds of the fatal habit of subsuming every element (sensation) under an unanalysed complex (p. 26), and this is admittedly a neat and sugges tive answer. It does not prove that there is nothing in that complex but its elements and their relations, but, on the other hand, the ego-advocates cannot prove that there is something. J. S. Mill reached this same stalemate, being unable to see how a chain of memories can be conscious of itself. ("Examination of Sir William Hamilton's Philosophy," particularly the chapter on the "Psychological Theory of an External World.") The fact is that we can no more circumnavigate and exhaustively comprehend the totality of our own self, than we can lift ourselves off the ground by pulling at our own bootstraps. It follows from this, and quite harmoniously with Prof, Mach's principles, that our attitude towards possible survival of death should be entirely noncommittal, so far as a priorism is concerned. He himself decides against it, somewhat vehementlywhich perhaps indicates human prejudice overcoming philosophic calm. But he writes for the most part with a saving humour and modesty, and in moments of quiet reflection he would probably admit that his "Weltanschauung" does not necessitate the annihilation of the large complex which is himself, when the portion of that complex which he calls his body is detached. (4) The Proceedings of the Aristotelian Society are for exceedingly athletic thinkers, and are probably the cause of many headaches even to them. The papers are highly technical, and in so far as they are philosophic rather than scientific, they do not call for detailed review in Nature. The present volume contains, among other things, the following: "Appearance and Real Existence," by G. Dawes Hicks; "William of Ockham on Universals," by C. Delisle Burns; "Philosophy as the Co-ordination of Science," by H. S. Shelton; "Intuitionalism," by N. O. Lossky; "Discussion -The Value of Logic," by A. Wolf and F. C. S. Schiller; "The Psychology of Dissociated Personality," by W. Leslie MacKenzie (who inclines too much to Münsterberg and Freud, and does not mention F. W. H. Myers); "Freedom," by S. Alexander; "The Status of Sense-Data," by G. E. Moore and G. F. Stout; and "The Principle of Relativity," by H. Wildon Carr, who discusses difficulties about the objectivity of the æther, etc., and finds absolute reality in life or consciousness itself only. (5) Probably no one can read M. Bergson without feeling the fascination of his style and the persuasiveness of his apt imagery; and the same is true of his chief disciple and expounder in this country. Mr. Carr gives us a sincere and careful account of the new philosophy as he sees it, emphasising its fundamental stress on change, and pointing out that with regard to science it is neither contemptuous like Hegelianism nor degraded to a servile co-ordinator as in the positivism of Comte and Spencer, but is equal and friendly, bringing a new method of its own for the attainment of further truth. This intuitional method requires a great effort at the outset, he admits; for it involves a turning away from the intellectual methods of the last 2500 years. After reading this book of Mr. Carr's and the whole of M. Bergson's published writings, one reviewer at least feels that while M. Bergson is undoubtedly trying to express what is very real and true to him and doing it in beautiful language-the thing is difficult and almost impossible, because the philosophy consists of an attitude, so to speak -or of a vividness of personal experience, which is incommunicable. Mr. Carr denies that it is mystical, and, taking some senses of that muchabused word, he is no doubt right; but it is mystical in its anti-conceptualism, and is essentially allied to various Oriental systems. It is a grafting of East on West, including the excellences of both. Perhaps at bottom it is a release from old fetters rather than a new doctrine. A heterodoxy does its chief good not by bringing new truth, but by cancelling out old error, and allowing the mind to go forward unencumbered. J. A. H. OUR BOOKSHELF. Panama, the Canal, the Country, and the People. By Arthur Bullard (Albert Edwards). Revised edition. Pp. xiv +601. (New York: The Macmillan Co.; London: Macmillan and Co., Ltd., 1914.) Price 8s. 6d. net. MR. BULLARD (Mr. Edwards of the first edition) has brought his sketch of Panama up-to-date by the addition of chapters describing the progress of the canal since 1911. The book consists chiefly of two parts, first a history of the State of Panama, and secondly a very pleasant description of the life of the Americans during the last ten years in the huge construction camp on the canal line. This life was well worth description, being truly a remarkable phenomenon. In the midst of a tropical wilderness, far from their own country, and in a pestilential climate, a labourcamp of fifty thousand hands settled at once to an orderly and civilised life, and, under the protection of a medical despotism, enjoyed on the whole excellent health. Mr. Bullard provides character sketches of the principal constructors-Colonel Goethals, Colonel Sibert, Doctor Gorgas, and the rest, including Mr. Comber, the dredging expert, who is responsible, under Colonel Goethals, for most of the work now going on. This consists in the removal of the material which comes into the Culebra cut from the breaking ground along a length of about two miles near the deepest part of the excavation. Part of it slides in from above, part of it squeezes up from below under pressure from the sides. It is this latter movement which is so disquieting. In one or two cases ships have gone aground before it was known that there had been an upheaval beneath the opaque and muddy waters of the canal. Some years may elapse before the Culebra cut is stable; meanwhile, the canal is used, though not without interruption, and the whole of the complicated lock machinery works without a hitch. V. C. Catalogue of Scientific Papers. Fourth Series. (1884-1900.) Compiled by the Royal Society of London. Vol. xiv. C--Fittig. Pp. 1024. (Cambridge University Press, 1915.) Price 2l. 10s. net. THE first volume of the fourth series of the Royal Society's Catalogue of Scientific Papers was noticed in the issue of NATURE for August 20 last. It was pointed out on that occasion that this series comprises the titles of papers published or read during the period 1884-1900, and concludes the work undertaken by the Royal Society. The catalogue thus completed will contain titles of papers for the whole of the nineteenth century. It will be remembered that the continuation of the work is now undertaken by the authorities of the International Catalogue of Scientific Litera ture. The present volume contains 24,994 entries of titles of papers by 4351 authors with the initial C, 17,665 entries by 3072 authors with the initial D, 7750 entries by 1368 authors with the initial E, and 6646 entries by 1230 authors under F, as far as Fittig. The total for the first two volumes of the series is 108,775 entries by 18,950 authors. It is to be hoped that the series of volumes will be added to every reference library of importance throughout the world, so that the public-spirited conduct of the publishers, who have undertaken the complete risk of printing and publishing, may not result in financial loss. What do We Mean by Education? By Prof. J. Welton. Pp. xii+257. (London: Macmillan. and Co., Ltd., 1915.) Price 5s. net. PROF. WELTON's question has been heard in every direction since the war began; and perhaps the outstanding characteristic of the answers which have been offered is the almost complete disagreement among them. Most competent persons will agree with Prof. Welton that "an investigation into fundamental principles" is necessary before a satisfactory reply to the question can be given. This book undertakes such an inquiry, and certainly the reader who follows the argument to the end will leave the volume with much clearer ideas on the subject. The titles of the chapters indicate the trend of the discussion: "The end rules the means"; "What should be the end?"; "Synthesis of liberty and authority"; "What are the means?"; "Who are the agents?" Though difficult reading in parts, the volume deserves the careful attention of teachers and educational administrators. LETTERS TO THE EDITOR. [The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURE. No notice is taken of anonymous communications.] The Spectra of Hydrogen and Helium. In a letter to NATURE of February 11, Prof. J. W. Nicholson discusses the recent interesting experiments of Mr. Evans on the spectrum emitted from a vacuum tube containing highly purified helium and subject to a heavy discharge. Evans found that the 4686 series and the Pickering series can be obtained in a helium spectrum showing no trace of the ordinary hydrogen lines. These series were observed a few years ago by Prof. Fowler by sending a heavy discharge through a mixture of hydrogen and helium; previously they had been observed only in star spectra. In addition, Evans observed that under the same conditions as the 4686 series and the Pickering series a new series of lines appeared, which, with regard to position and intensity, could be united with the Pickering series into a single series of the same type as the 4686 series. The lines of the new series have wave-lengths very close to the hydrogen lines of the Balmer series. In his letter Prof. Nicholson expresses the opinion that Evans's results cannot be used to discriminate between the different theoretical interpretations of the spectra in question, since the new series as well as the Pickering series can be deduced from the 4686 series on the general principle of combination of spectral lines. I cannot agree with this view, and should like here to state my reasons. According to the theory proposed by Rydberg, and generally accepted for a long time, all the lines in question are ascribed to hydrogen. This theory is based on a supposed analogy between the hydrogen spectrum and the spectra of the alkalies. The Balmer series, the Pickering series, and every second member of the 4686 series are considered as diffuse series, sharp series, and principal series. According to the theory proposed by the writer, the series spectrum of hydrogen is simply represented by the formula including the 4686 series, the Pickering series, and Evans's new series. K' is not exactly equal to K, though very nearly so, the theoretical value for the ratio K'/K being 1'00041. The theory rests upon a certain application of the quantum theory to the theory of the nucleus atom, and essentially involves the combination principle. While the ordinary helium spectrum is supposed to be emitted from a helium atom which has lost a single electron, spectrum (2) is emitted, according to the theory, from a helium atom which has lost both its electrons. If spark spectra result from the removal of two electrons from the atom, formula (2) should correspond to the spark spectrum of helium, while hydrogen, which is supposed to have only one electron in the atom, cannot give a spark spectrum. Since the numerical relations between the different series claimed by the two theories are not exactly the same, it would be possible at once, as mentioned by Prof. Nicholson, to discriminate between the theories if the wave-lengths of the lines were exactly known. It seems that both the measurements of Fowler and Evans are in close agreement with formula (2), but that it would be difficult to reconcile Evans's redetermination of the wave-length of the Pickering lines with Rydberg's assumption that the Balmer series and the Pickering series have the same limit. Quite apart, however, from the question of the exact numerical relationship between the series, it seems that fundamental difficulties in Rydberg's view are brought to light by the experiments of Fowler and Evans. Fowler's observation that the 4686 series contains twice as many members as the series predicted by Rydberg, and Evans's observation of the new series accompanying the Pickering series, destroy completely the simple analogy with the alkali spectra which forms the basis of Rydberg's theory. If, as Prof. Nicholson proposes, we look upon the Pickering series and the Evans series as a simple combination series deduced from the 4686 series, the contrast with the alkali spectra seems even more striking, since then apparently no sharp series is observed. On the other hand, it will be noticed that this simple relation between the series is an immediate consequence of formula (2), and that Evans's observation makes the representation of this formula more complete than before since only every second member of the series corresponding to n=4 was previously observed. I must confess, however, that perhaps the strongest objection to Rydberg's view seems to be the entirely different chemical conditions for the appearance of the Balmer series and the other series, so clearly shown by Evans's experiments. This difference has no analogy in the appearance of the diffuse series in the alkali spectra. I am afraid that it may not seem reasonable to emphasise this objection so strongly, since it, of course, has been contemplated by spectroscopists ever since the theory was proposed, but it appears that the basis for the consideration of this question recently has entirely changed. Rydberg's theory of the hydrogen spectrum offered not only an adequate representation of the evidence at hand at that time, but it was apparently the only way to bring the Pickering series into line with Rydberg's own fundamental investigations on the general relations between spectral series. However, Fowler's recent important work on series in spark spectra has shown that these spectra obey laws of exactly the same character as the ordinary arc spectra, with the only exception that the Rydberg constant is replaced by a constant four times as large. Consequently formula (2) corresponds to the general formula for series in spark spectra exactly as formula (1) corresponds to the general formula for series in arc spectra. It would therefore appear that at present there is scarcely sufficient theoretical evidence to justify us in disregarding the direct evidence as to the chemical origin of the lines given by Evans's experiments. It may be of interest in this connection to mention that the above conclusions seem to be supported by spectroscopic evidence of an entirely different character. Recently Dr. Rau (Sitz. Ber. d. Phys. med. Ges. Würzburg, 1914) has made some interesting experiments on the minimum voltage necessary to produce spectral lines. He finds that about 30 volts are necessary to produce the lines of the ordinary helium spectrum, and that the voltage necessary to produce the different lines and series in this spectrum differ only by a few volts. On the other hand, he finds that the lines of the Balmer series appear with 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 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 n and m 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 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 The constant k represents the a = 2k(ap(r) - by' (r)). action of the surrounding atoms and depends only upon the type of space-lattice formed by the atoms. is the same for all As the atomic frequency v=- I 2π a M isotopes, must be identical, whatever the 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. 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 pro proportional to afp(r)dr = bfy(r)dr, that is to M, as ris the same in both cases. The well-known equation A=RT2 dinp, where p is the vapour pressure, leads to dT' as the ratio of the vapour pressures, if the 68 chemical constant is equal. This is of the order e if M varies by 0-26 per cent, i.e. about 20 per cent. at 100° C. The vapour pressure of radium D the atomic 360 weight of which is 210 should be about e T times less than that of ordinary lead, that is, 2-6 times less at 100° C. Another posible test would be to measure the melting point. In a great many cases v=const. m T M As v cannot vary, and as Prof. Soddy has shown that ris constant, the melting point T should be proportional to M. Thus, for instance, the melting point of Prof. Soddy's lead should be 154° 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. |