of M. Bertrand, by M. Georges Ossian Bonnet.-Formulas giving the electric resistance of the circuit employed in the Edison system of electrical lighting, by M. G. Guéroult.-Observations relative to a method of studying earth currents, in connection with a communication recently made by M. Blavier, by M. F. Larroque. -Researches on the solidification of superfused sulphur (second part), by M. D. Gernez.-Determination of the equivalent of aluminium by means of its sulphate, by M. H. Baubigny.-On the formation of acetylene at the expense of the iodoform, by M. P. Cazeneuve.-New researches on the susceptibility of the eye to differences of luminous intensity, by M. Aug. Charpentier. -Cholera, small-rox, typhoid fever, and charbon amongst the coppersmiths of Villedieu, by M. Bochefontaine. Although the whole atmosphere of the place is, so to say, saturated with copper, nine of the inhabitants of Villedieu, all engaged in the copper industry, fell victims to cholera in 1849. Considering the difference of population, this would represent a mortality of 5700 in Paris. Nearly half of the population was attacked by small-pox in 1870, and a fatal case of charbon occurred in 1865.-On the existence and distribution of eleidine in the bucco-oesophagian mucous membrane of mammals, by M. L. Ranvier. On the genus Vesquia, a fossil yew found in the Aachen formations of Tournai, by M. C. Eg. Bertrand.-On a luminous phenomenon observed after sunset at Amiens on several evenings about the end of November and beginning of December last, by M. Decharme. The author feels inclined to attribute these effects to the aurora borealis. Details of similar manifestations observed in other places were quoted from a rec nt number of NATUre. BERLIN This Physical Society, November 30.-Dr. Kayser placed before the meeting a concave grating sent by Prof. Rowland to the Physical Institute, explained the principle of this apparatus, and exhibited a photograph of the normal spectrum produced by help of the grating, as also a negative prepared by Prof. Rowland, on which Dr. Kayser was able with the naked eye to count between the two H lines over seventy fine lines, among which some appeared to form groups, so that by means of a microscope many more lines still would be distinguishable.-Prof. von Helmholtz next gave a minute report of the continuation of the experiments he had instituted with a view to explaining galvanic polarisation according to thermodynamic principles. Suppose that an electric current passed through a liquid completely free of gas, then would the gases generated by decomposition of the electrolyte be first absorbed by the liquid, and only after the latter was saturated to a degree corresponding with the pressure of gas resting on it would the development of gas begin. The previous solution of gas in the liquid was the expression of an attraction or of a molecular energy between the water and the gas, which acted in the same direction as did the electromotive energy which decomposed the electrolyte at the electrode. The absorption of the gas, therefore, agreeably with the teaching of the mathematical theory, increased the electromotive energy, and all the more so the less gas the liquid contained. accorded with the experience derived from experiments that the convective current was so much the stronger by how much the less gas the fluid had absorbed. If the liquid already contained gas in solution, a part of it would escape at the surface by a kind of dissociation, and form above the liquid an atmosphere the pressure of which corresponded with that of the momentary saturation of the liquid. This dissociation of the solution represented a work which could reciprocally be applied to the conversion of gas to a liquid state; that is to say, supposing the conditions were such that the temperature of the system was maintained throughout unaltered, the whole process was a reversible one. With this consideration let one start from any normal condition whatsoever, from atmospheric pressure for example, then it was the teaching of the theory that the work was all the greater the less was the quantity of gas in solution, and in the case of very small gas volumes the work would be endless, that is to say, in every fluid were dissolved minute quantities of gas which could no longer be discharged. If the electrolytic fluid contained oxygen in solution, as in fact was regularly the case, the oxygen would be drawn by convection towards the oxygenous electrode, and there augmented by the oxygen which had been electrolytically separated, and after loss of its electricity be come neutral. The gas would now begin to diffuse itself towards the other, the hydrogenous electrode, and this diffusion would produce the polarisation current which, just as much as the diffusion stream, was opposed to the electrolytic current and convection. The quantity of oxygen in the fluid and its diffusion might be illustrated by a curve which ascended from the hydrogenous electrode as its zero point rectilinearly to the oxygenous electrode, and so long as the electromotive force remained the same at the electrodes a state of equilibrium was maintained between electromotive force, convection, polarisation current, and diffusion; a state of equilibrium which was disturbed when the current was interrupted for however short a time. The theory of these processes taught, what experience confirmed. that a much greater electromotive force was required after the interruption to re-establish electrolysis than was before needed to continue the process. If the fluid were saturated with gas to a degree corresponding with the pressure of gas resting on it, the gases generated by electrolysis escaped. Seeing, however, that the degree of saturation was dependent on the pressure of gas, therefore, with the increase of gas pressure, the electromotive force which caused the development of gas would likewise have to be increased. It was now sought to ascertain the least lectromotive force that was sufficient under a definite pressure to cause a development of gas, and the experiments made with this object in view showed that the development of the first bubbles had to overcome a considerable resistance, and therefore demanded intenser currents than were needed for later gas bubbles. When, by a definite current through an extended metallic wire, gas was developed in an electrolyte, by lessening the electromotive force it was possible to produce only single gas bubbles at one point of the wire. The same amount of electromotive force which was sufficient to produce this effect was not, however, equal to the generation of bubbles from the outset. To effect this latter result, a much stronger current would have to be employed. All these processes and relations here briefly indicated were mathematically calculated, and the results of the experiments invariably coincided with the teachings of the theory. .172 172 172 By Prof. 172 173 Lunar Rainbow.-C. H. Romanes; M. F. Dunlop American Wheat. By Prof. John Wrightson The Krakatoa Air-Wave. By General Strachey, F.R.S. Notes. Our Astronomical Column The Mass of Saturn Close Double-Stars Pons' Comet Tempel's Comet, 1867 II. 174 181 183 185 De Morgan's Five-Figure Logarithms Probable Nature of the Internal Symmetry of Crystals. By William Barlow (With Diagrams) The Helvetic Society of Natural Sciences. Notes from the Otago University Museum, IV. By Prof. T. Jeffery Parker (With Diagram) Scientific Serials. Societies and Academies THURSDAY, DECEMBER 27, 1883 VORTEX RINGS The Motion of Vortex Rings. By J. J. Thomson. (London: Macmillan and Co., 1883) BOTH OTH as regards the interest of the subject and the treatment it has received at the hands of the author we do not doubt that the essay before us is destined to take a foremost place amongst the essays which have been called forth, or at all events distinguished, by the Adams Prize. The fact that these essays are upon set subjects precludes the possibility of the prize being awarded for a distinctly original conception. It is almost a necessity that the subjects chosen should involve the extension of some mathematical investigation which has already been carried a certain length. The subject of the present essay is distinctly of this class; it involves an extension of the investigation of the theory of vortex motion in an ideal fluid, founded by Helmholtz and continued chiefly by Sir William Thomson. At the time Helmholtz conceived the fundamental principle, ideal hydrodynamics had no other interest, besides its mathematical interest, than it derived from the somewhat casual explanations it affords of the phenomena met with in the motion of actual fluids. Helmholtz's investigation had some relation to the observed phenomena of actual vortices, particularly to the phenomena of smoke rings, of which it afforded a general explanation. But between the fundamental equations which Helmholtz gave and their application to an actual vortex ring certain integrations were necessary, and these integrations presented mathematical difficulties. If we consider the line of smoke which forms the ring as indicating the portion of air in which vortex motion exists, we may say that the difficulties of integration at which Helmholtz stopped arise from the thickness of this line of smoke, or, calling this the circular core of the ring, from the finite area of the section of this core. Helmholtz contented himself with applying his theory to an indefinitely thin core; and the fact that the results of a theory based on a frictionless fluid would only have an imperfect relation to the motions of viscous fluids, together with the fact that such rings, although they may be produced by artificial apparatus, are short-lived, and have no existence in the general motion of fluids, offered but little inducement for farther prosecution of the subject. The case however was altered when it was conceived by Sir William Thomson that the atoms of matter may be such rings moving in a perfect universal fluid. Smoke rings, although their behaviour seems to have suggested the idea, could not, owing to the viscosity of the air, by any means be made to afford an experimental | verification of the capabilities of such an hypothesis. The only way was to integrate Helmholtz's equations, and thus arrive at the theoretical behaviour of such rings. Unfortunately the mathematical difficulties are such that there is little hope of obtaining a complete theory of vortex rings having cores of any finite area. Sir William VOL. XXIX.-No. 739 Thomson, however, started an approximate theory as a step towards this; he succeeded in approximately integrating the equations for rings the cores of which had sections finite but small compared with the openings of the rings, and with such rings it appears that his theory can be tested as regards matter in the gaseous state. To do this, however, it is necessary to do more than work out the theory of a single circular ring having a core of circular section. The phenomena of gases depend on the internal vibration of the atoms and on the influence which they exert on each other by collisions or otherwise. It was necessary therefore to obtain the theory of the vibrations of these rings, also of the effect of what may be called collisions. Sir William Thomson took many steps towards the theory of vibrations. But the theory of collisions was left for Mr. J. J. Thomson. Mr. Thomson has not, however, confined his attention to the point set for the prize, but, starting from the foundation laid by Helmholtz, has recast the theory to his own method. Having deduced general expressions for the momentum, moment of momentum, and energy in a mass of fluid in which there is vortex motion, which expressions are better adapted for his purpose than any previously obtained, he proceeds to the theory of a solitary vortex ring subject to the same limitation as that treated by Sir William Thomson, i.e. the diameter of the core small compared with the opening of the ring, but of more general shape, in that it may have any small deviation from the circular form. He obtains results which, where they correspond, agree very approximately with those previously obtained by Sir William Thomson. The author then proceeds to the immediate subject of the essay the action upon each other of two rings. In dealing with this subject he introduces another important limitation, i.e. that the rings shall not approach each other by a distance which is large compared with the openings of the rings. With this limitation, by means of a very powerful piece of mathematical work, the theory of the mutual action of such rings is deduced, both as regards mean motion and. vibration; and he has thus carried the theory of vortex atoms to such a stage that in certain general respects it can be applied to the theory of gases. The essay, however, does not end here, for, although outside the set subject, the author proceeds to consider the theory of "linked rings." This term does not seem well chosen, for it conveys the idea of rings linked as in a chain, whereas what it is used to express is a ring of which the core is compounded of several separate cores wrapped in a spiral manner round each other like a ring composed of twisted wire. In the treatment of this branch of his subject he has been no less successful than in the earlier parts. From the general scheme of his essay it is clear that the author has had in his mind as a general object the verification of the vortex atom theory; and although he avowedly refrains from going at length into such a vortex atom theory of gases as might be built upon his work, he adds a chapter at the end in which he discusses certain results of his work, which may be applied without further calculation to the vortex atom theory of gases. K It is this chapter which will excite the most general interest, for although the fact of this still very incomplete theory being found consistent with observed gaseous phenomena would not afford a crucial test of its fitness to explain the phenomena of solids and liquids, still its failure to explain the phenomena of gases would appear to be crucial as regards its unfitness as an atomic theory. The fair and cautious spirit in which Mr. Thomson discusses his results cannot be too much admired, although we may not be quite able to realise the truth of his reasoning. *The most general and important phenomenon of gases is that sometimes called Boyle's law-that the product of the volume and pressure of any fixed weight of gas varies directly as the amount of heat, i.e. kinetic energy, in a gas. Accordingly Mr. Thomson calculates the product of the pressure and volume which would result in the case of a vortex atom gas. This he finds equal to two terms. one being the kinetic energy multiplied by a constant, the other a certain quantity which involves the squares of the velocity of the medium at the boundary surface. To fit Boyle's law this second term must vanish or nearly so. Mr. Thomson argues that it does so vanish, because the surface being at rest the velocity of the fluid at it must be small. This argument we entirely fail to follow, possibly owing to some misapprehension on our part; but it seems to us that a vortex being near a solid surface is no reason for supposing the tangential velocity of the fluid small, while if the gas consists of vortex atoms so must the solid surface, and there is nothing to show that the mean square of the velocity within the solid and at its surface will be less than in the gas. Passing on from Boyle's law, with the explanation of which he is satisfied, the author next turns to the phenomena depending on the velocity of the gaseous molecules. As this seems to us the most interesting part of the dis cussion, we quote the passage in full : "According to the vortex atom theory, as the temperature rises and the energy increases the mean radius of the vortex rings will increase, but when the radius of a vortex ring is increased its velocity is diminished, and thus the mean velocity of the molecules decreases as the temperature increases; thus it differs from the ordinary kinetic theory, where the mean velocity and the temperature increase together. It ought to be remarked, however, that though in the vortex atom theory the mean velocity decreases as the temperature increases, yet the mean momentum increases with the temperature. "The difference between the effects produced by a rise in temperature on the mean velocity of the molecules will probably furnish a crucial experiment between the vortex atom theory and the ordinary kinetic theory of gases, since all the laws connecting the phenomena of diffusion with the temperature can hardly be the same for the two theories. In fact, if we accept Maxwell's reasoning about the phenomenon called 'thermal effusion' we can see at once an experiment which would decide between the two theories. "The phenomenon is this, if we have a porous diaphragm immersed in a gas, and the gas at the two sides of the diaphragm at different temperatures, then when things have got into a steady state the pressures on the two sides of the diaphragm will be different, and Maxwell, in his paper On Stresses in Rarefied Gases' (Phil. Trans. 1879, part i. p. 255), gives the following reasoning to prove that, according to the ordinary theory of gases, the pressures on the two sides are proportional to the square root of the absolute temperatures of the sides. He says: "When the diameter of the hole and the thickness of the plate are both small compared with the length of the free path of the molecule, then, as Sir W. Thomson has shown, any molecule which comes up to the hole on either side will be in very little danger of encountering another molecule before it has got fairly through to the other side. "Hence the flow of gas in either direction through the hole will take place very nearly in the same manner as if there had been a vacuum on the other side of the hole, and this whether the gas on the other side of the hole is of the same or of a different kind. "If the gas on the two sides of the plate is of the same kind but at different temperatures, a phenomenon will take place which we may call thermal effusion. The velocity of the molecules is proportional to the square root of the absolute temperature, and the quantity which passes out through the hole is proportional to this velocity and to the density. Hence, on whichever side the product of the density into the square root of the temperature from the other through the hole, and this will go on till is greatest, more molecules will pass from that side than this product is equal on both sides of the hole. Hence the condition of equilibrium is that the density must be inversely as the square root of the temperature, and since the pressure is as the product of the density into the the square root of the absolute temperature.' temperature, the pressure will be directly proportional to "If we were to apply the same reasoning to the vortex atom theory, we should no longer have the velocity proportional to the square root of the absolute temperature, but to some inverse power of it, and the above reasoning would show that if pand be the pressures, t and t'the temperatures on the two sides of the plate, p\p' = (t\t')”, where m is a quantity greater than unity. Thus accurate investigations of the phenomenon of thermal effusion would enable us to decide between the vortex atom and the ordinary kinetic theory of gases. These experiments would, however, be difficult to make accurately, as we should have to work with such low pressures to get the mean path of the molecules long enough that the pressure of the mercury vapour in the air-pump used to rarefy the gas might be supposed sensibly to affect the results. In the theoretical investigation, too, the effects of the boun ting surface in modifying the motion of the gas seem to have scarcely been taken sufficiently into account to make the experiment of the crucial test of a theory; and it is probable that the theory of the diffusion and viscosity of the gases worked out from the laws of action of two vortex rings on each other, given in Part II. of this essay, would lead to results which would decide more easily and more clearly between the two theories. "The preceding reasoning holds only for a monatomic gas which can only increase its energy by increasing the mean radius of its vortex atoms; if, however, the gas be diatomic, the energy will be increased if the shortest distance between the central lines of the vortex cores of the two atoms be diminished, and if the radius of the vortex atom is unaltered the velocity of translation of the molecule will be increased as well as the energy; thus for a diatomic molecule we cannot say that an increase in the energy or a rise in the temperature of the gas would necessarily be accompanied by a diminution in the mean velocity of its molecules." With the argument here used we have no fault to find, but it does seem to us that the author has fallen into some confusion between the experimental phenomenon of thermal transpiration through porous plugs and the theoretical idea of "thermal effusion." It has probably escaped Mr. Thomson, but the experiment he suggests was included in the general investigation, made by the writer of the present review,' by which the phenomenon of thermal transpiration was discovered, and although it still appears that these are the only experiments on this subject, yet they conclusively prove that the difference of the pressure on the two sides of the plate is proportional to the square roots of the absolute temperatures. So far then it would seem that the crucial experiment has been made and that the verdict is against the vortex atom theory; but this is not so, for, although the experiment Mr. Thomson suggests has been made, it is definitely and experimentally shown in the same investigation that the action of the porous plug is entirely different from that which Maxwell calls thermal effusion, being due entirely to the tangential action of the walls of the passages, and further this tangential action is in strict accordance with the present dynamical theory of gases. This experiment with the porous plug, then, affords no test whatever in the way suggested by Mr. Thomson. Mr. Thomson has, we think, been unfortunate in his choice of tests; and we would suggest the velocity of sound as affording a crucial test for which the experimental work is already done. It appears to be an almost obvious deduction from the vortex atom theory that the velocity of sound must be limited by the mean velocity of the vortex atoms; and since Mr. Thomson has shown that this mean velocity diminishes with the temperature, while experimentally it is found that the velocity of sound increases as the square root of the temperature, it appears that the verdict must be against the vortex atom theory. However the vortex atoms are very slippery things, and we should like to hear Mr. Thomson's opinion before adopting one of our own. Besides discussing the theory of gases, Mr. Thomson goes somewhat fully into a vortex atom theory of chemical combinations; in this he raises many points which will doubtless be of great interest should the hypothesis survive the crucial test by the theory of gases which this essay now for the first time renders possible. Of the mathematical interest of the essay we can only say that to those who can appreciate it this will be found to be very great. OSBORNE REYNOLDS OUR BOOK SHELF through the entire series of processes: stereographic projection, assignment of indices, calculation of elements, and recalculation of angles, each given in its place as an example of the principles and formulæ employed. This practical illustration is a far more effectual means of recommending the methods to the reader than mere verbal description. It will probably be found that these methods of calculation are the most valuable part of the book; they are so systematically arranged and tabulated that the various cal error must be detected at once, while much labour is steps may be distinguished at a glance, and any numerisaved by the methodical order in which the operations are conducted. It is to be presumed that the laborious process of calculating the angle between each pair of faces from the elements by means of the general formula is given as an exercise in the method of least squares rather than as an example of the course to be actually adopted in any but rare cases. One subject, however, of some importance is barely touched upon; namely, the criticism of images obtained from crystal faces on the goniometer, and their interpretation. Both in the descriptive paragraphs and in the above-mentioned illustration, all measurements of the same angle upon different crystals are assumed to be equally good, so that their arithmetic mean is adopted as the observed value, whereas the difficulties presented by multiple images seem to deserve treatment in a book which deals so exhaustively with the practical side of the subject. It is to be regretted also that the discussion of optical properties and measurement has been almost crowded out of the work. H. A. M. 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. No notice is taken of anonymous communications. [The Editor urgently requests correspondents to keep their letters as short as possible. The pressure on his space is so great that it is impossible otherwise to insure the appearance even of communications containing interesting and novel facts.] The Remarkable Sunsets SPEAKING of Virginia City, the great silver mining centre of Nevada State, I said, in "An Engineer's Holiday," that it "lies among the foothills of the Sierra, at an elevation of 6200 feet, on the eastern face of Mount Davidson . . . surrounded by innumerable interlocked mountains, conical in outline, red-brown in Krystallographische Untersuchungen an homologen und colour, and perfectly bare of all vegetation. These stretch, as isomeren Reihen. Von Dr. A. Brezina. I. Theil. Methoden. (Wien, 1884.) THIS very useful volume forms an introduction to the author's crystallographic investigations which earned the prize of the Vienna Academy. It deals exclusively with the principles and the methods employed in those investigations, and constitutes a complete storehouse of the formulæ required in the study of crystals, and of the best means of applying those formulæ. The following subjects are successively treated: the optical principles involved in the goniometer; the practical use of the instrument, and the errors to which it is liable; the criticism of probable errors of observation; stereographic projection; all possible cases of trigonometrical calculation, including the method of least squares; and a slight sketch of the use of the polarising apparatus. An important feature of the book is the illustration of methods by the actual measurement of seven crystals of a triclinic substance. The readings of the goniometer scale are first given, and from these the reader is led "Certain Dimensional Properties of Matter in the Gaseous State," Phil. Trans. 1879, Part II. far as the eye can reach, to where the snowy tops of the Hum. boldt peaks stand against the sky, and the terrible sterility of the scene is enhanced rather than relieved by the thin meanderings of the Carson River, whose course is marked by a narrow green line. This is the only sign of water visible in the arid panorama, whose bare, red cones are steeped all day in dusthaze, and lighted for a few minutes at sunset by an Alpenglow' which dyes the countless peaks in as countless gradations of rosy light." It certainly did not occur to me, when I wrote the above three years ago, that the finer and higher particles of the dusthaze which obscures the dry air of the American desert may have been concerned in producing the splendid sunset effects which I witnessed at Virginia City; but this, after our recent experiences, seems very probable. D. PIDGEON Holmwood, Putney Hill, December 22 I HAVE received a letter, dated December 5, from Mr. Joseph Moore, of New Garden, North Carolina, U.S.A., in which he informs me that "the phenomena at both sunset and sunrise have been unusual in more than a dozen instances here during the autumn. Only the night before last we had an extraordinary sunset. The sky bore all the tints of which you speak, but I do IN a letter dated Tokio, October 3, describing a tour in the interior of Japan, Prof. James Main Dixon writes:- During the two or three days at the end of August we enjoyed fine dry weather, but the sun was copper-coloured and had no brightness. It was capital weather for travelling, but rather inexplicab'e. When we got to Nikko, the people came to us to inquire if some catastrophe were impending, for the appearance of the sun foreboded evil. We laughed at their fears, and assured them all was right. However it seems that if the appearance of the sun foreboded no evil, it was a wonderful sign of the greatest earthquake and volcanic catastrophe on record. The fearful explosion of Krakatoa, in the Straits of Sunda, took place on August 26, and there seems little reason to doubt that the monsoon had carried the volcanic dust along with it, the dust obscuring the sun. The distance is nearly 3000 miles." LEWIS CAMPBELL St. Andrews, December 22 Peripatus DR. VON KENNEL, in a note on the "Development of Peripatus," which appeared in a recent number of the Zoologischer Anzeiger, and has been translated and printed in your columns, has thrown some doubt on the accuracy of the observations recorded in the late Prof. Balfour's memoir on the "Anatomy and Development of Peripatus capensis (Quart. Journ. Micro. Sci., April, 1883). We trust that you will give us, as the editors of that memoir, this opportunity of making a few brief statements in reply to the somewhat unusually outspoken criticisms contained in his preliminary note. Dr. von Kennel entirely omits to mention in his paper that Prof. Balfour's researches refer to a Cape species of Peripatus AP. capensis), whilst the species which he has worked at are West Indian, and differ considerably from Peripatus capensis. Considering the fact, well known to embryologists, that there are numerous instances of great discrepancies in the embryonic history of closely-allied forms, it seems to us strange that the only explanation, suggested by Dr. von Kennel, of the differences between his results and those recorded in Prof. Balfour's memoir should be that the latter are absurdly erroneous. The remarkable attitude which Dr. von Kennel has assumed in this matter must have been obvious to all competent zoologists. We offer these remarks mainly because his statements have appeared in a journal which has a wide circulation amongst readers who are not so well able to judge of the merits of the case. We are able to state in conclusion that the results enumerated on pp. 256, 257 of Prof. Balfour's memoir have been confirmed by Mr. Sedgwick on a large number of fresh and well-preserved embryos of Peripatus from the Cape, obtained since the publication of the memoir. H. N. MOSELEY A. SEDGWICK [THE translator of Dr. von Kennel's "Note on the Development of Peripatus," to whom we submitted the above letter, writes to us that, "though with a large experience in such matters, he is quite unable to see anything unusually outspoken'in Dr. von Kennel's criticisms; had any such occurred, he would have passed them over; nor does he find any foundation for the statement that Dr. von Kennel explains the results of Prof. Balfour's memoir as 'absurdly erroneous.' Dr. von Kennel, at the beginning of his note, only asserts that his observations cast some doubt on those of Balfour, apologetically adding that his material was immensely richer than Balfour's, and at the conclusion of his Note he simply calls attention to the discrepancies between his observations and Balfour's illustrations." At the translator's request we quote the original of the two critical paragraphs with the translations, so that the many competent zoologists who are amongst our readers can judge whether the latter adds to or takes from the spirit of the former.-ED. NATURE. "Ich thue dieses hauptsächlich deswegen, weil die durch Moseley und Sedgwick publicirte Abhandlung aus dem Nachlass Balfour's einige Abbildungen von Embryonen und Schnitten durch solche enthält, deren Genauigkeit ich nach meinem reichlichen und ausgezeichnet conservirten Material und nach den Beobachtungen am frischen Objecte etwas anzweifeln muss, deren Deutung vollends die Probe nicht hält." "I do this chiefly because the treatise published by Moseley and Sedgwick from the posthumous notes of Balfour contains some representations of embryos and cross-sections of the same, upon whose accuracy in details I, with my rich and well-preserved collection of specimens, and observations or fresh objects, must cast some doubt, and the interpretation of which does not bear investigation." "Ich enthalte mich hier, um nicht weitläufig zu werden, jeder Discussion, muss jedoch noch einmal darauf hinweisen, wie wenig Balfour's Abbildungen und die Schilderungen der Herausgeber mit den hier mitgetheilten Thatsachen stimmen." "I here abstain for the sake of brevity from all discussion, but must, however, call attention to the fact how little Balfour's illustrations and the descriptions of the Editors agree with the facts as they are here given."] A New Rock DURING my visit last summer to Lake Sagvand, in the Balsfjord, near the city of Tromso, I discovered a new enstatitebearing rock, which forms entire little hills. It is composed of light yellow green enstatite, mixed with magnesite. The magnesite, which is entirely free from lime, is partly white, partly dirty grey in colour, in which latter state it contains a little oxidulated iron, and appears then distinctly crystalline, with rhomboidal planes of cleavage. The rock is greatly interspersed with little grains of chromite, which are found in the enstatite as well as the magnesite. Here and there small grains of pyrite also appear. The substance is perfectly free from olivine, at all events neither olivine nor serpentine has been discovered under microscopical analysis. The rock must be considered a new petrographical species. I have named it "Sagvandite," from the place where it was first discovered. It appears with a strong reddish-brown colour on its uneven surface, where the magnesite is completely washed out, so that the enstatite alone remains. The rock is not slaty, and must so far be said to be of massive structure. When I have had an opportunity of thoroughly analysing the new substance, I propose to give a complete description of it in NATURE. KARL PETTERSEN Tromso Museum, Finmarken, Norway, December Diffusion of Scientific Memoirs IN his notice of the Reprint of Prof. Stokes' papers in NATURE for Dec. 13 (p. 145), Prof. Tait, with characteristic incisiveness, speaks of the "almost inaccessible" volumes of the Cambridge Philosophical Transactions, and proceeds to offer an 'easy cure" for that simple though grave malady. I think if Prof. Tait had taken the trouble to make the inquiry he would have found that very few societies are so liberal in the free dissemination of their publications, and that the number of universities, prominent societies, or libraries which do not receive them gratis, or merely in exchange, is very small. December 14 W. M. HICKS THE question so pointedly at issue between Mr. Hicks and myself is one which can be settled by statistics only. NATURE would do a real service to science by collecting statistics as to the numbers of different centres (home, and foreign, separately) at which the Transactions of various scientific Societies were freely accessible in 1883 (say); and also the corresponding numbers in 1853. The Royal Society regularly publishes such information in its Transactions, so does the Royal Society of Edinburgh. I have been a Fellow of the Cambridge Philosophical Society for about 30 years; and, during that time, I have received from the Society some fasciculi (of Proceedings only) certainly not amounting to a dozen in all :—and I am not aware that my case is an exceptional one. Mr. Hicks writes as if he thought I was bringing an accusation. Surely the figure, of malady, which I was careful to employ, cannot be so construed. P. G. TAIT |