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valve setting, and turbine valve mechanisms and governors.

The volume is noteworthy for the clearness of the drawings (mostly taken from working drawings), and for the lucidity of the text. It is difficult, however, to state what precisely would be its position in the engineering courses at colleges in this country. This is owing to the matter being almost wholly descriptive. Students of engineering learn best by doing, not by merely listening or reading. Numerous valve diagrams are given, but no student desires to copy these, and no definite exercises are given to be worked out by the student himself. As a minor matter, we may point out that it would have been an advantage if even one leading dimension had been inserted in the detail drawings. It is difficult for beginners to sort out which devices are suitable for large and which for small engines. The book, however, can be recommended to any student who wishes to improve his knowledge of the construction of valve and governor details.

Reports from the Laboratory of the Royal College of Physicians, Edinburgh. Edited by Dr. J. J. Graham Brown and Dr. J. Ritchie. Vol. xviii. (Edinburgh: Oliver and Boyd, 1915.)

THE directors of every research institution have to face a peculiar difficulty connected with publication. In issuing an account of the various inquiries conducted in the laboratories under their charge two modes of publishing are open to them. They may issue a special report, or they may allow the workers in the laboratories to contribute their results to appropriate professional journals or proceedings of societies. A special report is expensive; it does not secure the ear of the scientific public so well as professional journals do. The laboratory of the Royal College of Physicians in Edinburgh has combined these two methods; it has collected the papers contributed to various journals by its workers during 1913-14, and issued them as the thirteenth volume of its Reports. In all there are thirty-two papers, every one of them representing a definite contribution to the basal subjects of medicine. Four papers give an account of the researches of Dr. J. P. McGowan into the nature of sarcocyst, associated with the disease of sheep known in Scotland as "Scrapie." Four papers are devoted to human anatomy, Dr. J. S. Fraser's sections of the inner ear being of particular merit. The remaining papers are devoted to biological chemistry, pathology, and bacteriology. We note particularly the research carried out by the late Dr. Alexander Brucewhose death was a serious loss to British neurology and Dr. James W. Dawson on a curious form of tumour which occurs in the central nervous system. A study of the minute structure of these neuromata supports the multicellular theory of nerve-fibres. Dr. D. P. B. Wilkie's important observations on the clinical signs of acute obstruction of the appendix vermiformis as distinguished from acute inflammation of the appendix also appears in this volume of

reports. The thirteenth volume is one on which is editors, Dr. J. J. Graham Brown and Dr. James Ritchie, superintendent of the laboratory, may be warmly congratulated.

The Poison War. By A. A. Roberts. Pp. 144 (London: W. Heinemann, 1915.) Price 5s. net MR. A. A. ROBERTS, who is described as a member of the Chemical Society of France and also of the Society of Chemical Industry, has given the public a book to which no one with any chemical knowledge will deny the epithe: remarkable." Two or three short extracts from its pages will perhaps best illustrate its value.

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On page 57 we find "The white smoke referred to, upon the explosion of German shells, is caused by the union of phosphoric and phosphorus acids with the oxygen of the air." Oa page 90 we are told: "Toluene is a colourless liquid obtained from resins such as tolu: the latter being the product of a South American tree. Some of the medicinal preparations of this resin are well known to the public, as 'Balsam of Tolu' and Friars Balsam. In reference to guncotton, on page 91 we learn: "Reverting to the subject of gun-cotton, this explosive is now made by soaking cotton or waste in nitric acid. Cotton is indispensable, as it absorbs the oxygen and nitrogen contained in the acid, and is a combustible substance." On page 98 we read: "Nitro-glycerine, or even gun-cotton, if burnt in an open vessel, will not explode, but the moment they are fired by detonation explosion follows, the explosion being due to decomposition." The non-poisonous character of nitro-glycerine is illustrated by the following statement on page 99: "A laboratory employé, in another instance, partook of two ounces of nitro-glycerine, mistaking it for chocolate, and on the morrow was none the worse for his stupidity."

Indian Mathematics. By G. R. Kaye. Pp. 73(Calcutta and Simla: Thacker, Spink and Co., 1915.)

MR. G. R. KAYE's booklet gives a summary of the actual contents of Indian mathematical works, translations of original passages, an approximate chronology, and a bibliography. The net result of recent work in this field is to reduce still more the claims once made on behalf of Indian mathematicians, both in respect of priority and in that of originality; two main questions are still unanswered-who invented the decimal notation now current, and what is the complete history of the Pellian equation? Mr. Kaye suggests that India is probably indebted to China for some of its analysis, just as it is certainly to Greece for its geometry (in Arabic translations or otherwise); it is to be hoped that Chinese documents will be forthcoming to throw light on these and other matters. Meanwhile, such a work as this of Mr. Kaye's is very useful as a trustworthy conspectus of what is actually known about early Indian mathematics at present.

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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 Structure of Magnetite and the Spinels. THE structure of the spinel group of crystals is very interesting. These crystals are cubic, and possess the greatest possible number of symmetries. The composition is given by the formula, R"R"",O,, where the divalent metal R" may be Mg, Fe, Zn, or Mn, and the trivalent metal R" may be Fe, Mn, Cr, or Al. Magnetite is FeFe,O,.

The structure is fundamentally the same as that of the diamond. Each carbon atom of the diamond is to be replaced by the divalent metal atom; the distance between two neighbours being 3.60 A.U. in magnetite as against 1.53 A.U. in diamond. The four oxygen atoms are arranged in a regular tetrahedron about the divalent atom. The lines joining the latter to the former are parallel to the four cube diagonals. Any two neighbouring tetrahedra point towards each other. If each perpendicular from a tetrahedron corner on the opposite face is produced it encounters another tetrahedron, passing first through the middle point of a face and then through the opposite corner. A trivalent atom lies on each such connecting line, half-way between the tetrahedra. The distance between a divalent and the nearest trivalent atom is 7.20 A.U. Four trivalent atoms are associated with each tetrahedron, but each atom is shared by two tetrahedra. As in other cases already examined, the molecule has no separate existence. The size of the tetrahedron may not be the same in all members of the group of crystals. The divalent atom lies at the centre of a tetrahedron of oxygen atoms, and the trivalent at the centre of an octahedron.

Leeds, July 12.

W. H. BRAGG.

The Magnetic Storm of June 17, and Aurora. PROF. BARNARD'S interesting letter dated June 25, in NATURE of July 15, on what is termed "The Great Aurora of June 16, 1915," is at first sight rather puzzling to the non-astronomical reader. The large magnetic storm began about 1.50 a.m. on June 17. On June 16, it is true, there was a magnetic disturbance, but not such as to suggest a striking auroral display. The explanation presumably is that Prof. Barnard is referring to an astronomical day, commencing at Greenwich noon on June 16. This, at least, would explain his statement that at Wisconsin (about 90° W.) at 21h. 25m. the sky was bright with dawn." This one would expect between 3 and 4 a.m. local time. If this is correct, then the first auroral appearance chronicled by Prof. Barnard was at 3.30 a.m. on June 17, Greenwich civil time, and the maximum brilliancy about 8.15 a.m. It was principally during these morning hours that the Kew magnetic curves had the rapid oscillatory character usually associated with aurora and earth currents. The newspaper reports quoted by Prof. Barnard seem to fit this explanation.

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date, storm or no storm, the chances are Father Cortie could supply a spot. I think Father Cortie has not quite grasped my argument that quiet days show the twenty-seven-day period equally with disturbed days, and that one can scarcely associate them with limited areas or "anti-spots." If one associates them, as he now seems to do, with an undisturbed state of a whole solar hemisphere, why not equally associate storms with a generally disturbed state of a whole hemisphere? As a matter of fact, the average quiet day seems associated with a practically average state of solar spottedness. The 600 quiet days selected by the Astronomer Royal from 1890 to 1900 gave for Wolfer's provisional sun-spot frequency a mean value of 41-28, the mean from all days of the eleven years being 41-22. They showed the twenty-seven-day period very clearly. C. CHREE.

Richmond, Surrey, July 17.

Surface Tension and Ferment Action.

IN NATURE of June 17 Messrs. E. F. and H. E. Armstrong criticise the conclusions drawn by Mr. Beard and myself in a paper published in the Proc. Roy. Soc. of June 1, under the title "Surface Tension and Ferment Action." We drew the conclusion that the action of invertase was inhibited by surface tension. According to Messrs. Armstrong the inhibition observed under the conditions of our experiments was due simply to a minute trace of alkali given off by the glass. They state in confirmation of their view that the action of the alkali given off by ordinary glass is so marked that it is impossible to obtain consistent results with invertase, unless hard glass vessels, test-tubes, and storage bottles are used. That is certainly not our experience. We failed to find any difference in the readings between two mixtures of cane-sugar and invertase, of which one was kept in contact with glass beads at medium temperatures, as long as the amount of invertase used was relatively large. Our experience in that respect is apparently in accordance with that of Sörensen, who states that the effect of the alkalinity of glass makes itself felt only in the case of invertase solutions which have been especially purified.

In our experiments an inhibition was noticed only when the amount of invertase was relatively small. Under these conditions an alteration in the hydrogenion concentration produced by the minute trace of alkali given off by glass may have had some share in producing an inhibition, but it does not account for certain features of the phenomenon, which we have been careful to emphasise in our paper. If the alkali from the glass was entirely responsible for the effect one would expect the inhibition to persist in its entirety after the glass beads have been removed. This was found not to be the case. Again, the weakening of an invertase solution, which had been allowed to stand in contact with glass beads at medium temperatures and which we ascribed to absorption of the ferment by glass, cannot be explained on the ground put forward by Messrs. Armstrong. Their view necessitates the assumption of so large an amount of alkali given off by glass to an invertase solution, that it should be detectable by such an indicator as phenolphthalein. This again was not the case.

The interruption of my work has unfortunately delayed the completion and publication of similar observations with diastase carried out by Mr. McCall and myself. It was found that the inhibition produced by extending the surface-glass water could be almost completely removed by coating the glass with a thin film of a surface-active substance, such as methyl alcohol, ethyl alcohol, amyl alcohol, ether. On the other hand, films of ligroin and xylol deposited on the glass failed to remove the inhibition.

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WE

E give in another column the names of the members of the Inventions Board which is assisting the Admiralty in the co-ordination and encouragement of scientific effort in relation to the requirements of the Naval Service. The Central Committee and the Panel of Consultants form as strong a body of expert opinion as it would be possible to bring together; and their judgment upon scientific matters submitted to them may be accepted with confidence. Suggestions and inventions sent to the Admiralty will, if they relate to naval matters, first be considered by officials of the existing staff, and any promising ideas or devices will be passed on to the Central Committee, consisting of Lord Fisher, Sir J. J. Thomson, Sir C. A. Parsons, and Dr. G. T. Beilby. This committee, when necessary or desirable, will refer particular points to members of the panel of consultants, which includes leading workers in chemistry, physics, metallurgy, and various branches of engineering science. The president of the Royal Society is one of the consultants, and with one exception all the other advisers are fellows of the society, which is thus giving of its best to the service of the country.

Since the early days of the war the Royal Society has been in close touch with the naval and military authorities with regard to scientific problems presenting themselves in the course of the operations. In the autumn the Council set up an organisation which has been expanded in various directions to meet the continually increasing requirements of the Government for scientific assistance. It consisted essentially of a general controlling committee, which was at first appointed ad hoc, but is now the Council itself; and sectional committees, each of which represents one of the several branches of science concerned, namely chemistry, engineering, physics, and physiology. Each committee has been placed by the council in charge of a chairman of acknowledged eminence. The Governmental de

partments concerned have nominated special rep sentatives who sit as members of the section: committees, and through them and the committer: own officers confidential relations have been esta lished with those departments. The committe also are in touch with the scientific instituti and manufacturing centres throughout country. These committees as working bodare necessarily limited in size, having regard the very confidential nature of the subjects su mitted to them; but they avail themselves large as circumstances require, of the services of vestigators outside their own membership.

The value of the work thus accomplished w publicly recognised by the Prime Minister late in his remarks in the House of Commons. B though the Government has acknowledged the scientific men have rendered valuable assistan in connection with problems arising out of the war, no definite scheme seems yet to exist for the organisation of our scientific forces into : composite body. The Chemical Society, as me announced on July 8, has taken steps of its own accord to form a consultative council upon whic kindred societies such as the Institute of Chemistry, the Society of Chemical Industry, the Society of Public Analysts, the Pharmaceutical Society, and the Institution of Mining and Metallurgy will be represented. Scientific and industrial knowledge and interests are thus intimately associated, as they should be, but the relation of this group of chemical societies to the Physical Society, which has also formed a committee to consider suggestions and inventions, or to the war com mittees of the Royal Society, does not appear to have been settled. Unless there is close co-operation between the committees of the various scientific societies it is difficult to see how overlapping will be prevented or how combined expert knowledge can be concentrated upon physica, chemical, and engineering problems requiring early and practical solution.

In addition to appointing committees to consider suggestions or inventions, the Royal, Chemical. and Physical Societies have taken steps to obtain registers of their fellows classified according to special knowledge and to scientific services which the fellows are willing, as well as specially quali fied, to perform. The idea in each case is to secure co-operation among the fellows of the particular societies, and to examine by means of committees any promising suggestions relating to munitions of war or kindred subjects. No one knows precisely what will be done with the registers when they have been completed. Each society seems to be compiling its list independently and without any clear view of the use which will be made of the experts' services which will become available by the response to its circular. No scheme has yet been put forward by which definite national duties will be assigned to the hundreds of scientific men who are enrolling themselves on the registers of their respective

societies.

The case is different with men who are

apable of taking their places in workshops. register of the names and addresses of all ersons who are willing to devote either the whole r some definite part of their time to industrial ervice of the kind indicated is being made at any engineering laboratories, so that no one with ny mechanical aptitude need now lament absence f opportunity of employment in national work. In a number of engineering laboratories of niversities and technical colleges in different arts of the country, short courses are now being onducted by means of which, for a nominal fee, reliminary training can be obtained which will nable suitable persons to be recommended by the Local Munitions Committees for employment in he manufacture of munitions of war. Practical experience of employers has shown that comparaively unskilled assistance may materially increase he output of munitions in a district. Of course, persons who have already had some experience in dengineering workshops can render more effective service than those who lack such experience; but there is much work to be done on machines which are so arranged that unskilled men or womencan use them after very little preliminary training. The classes arranged in engineering laboratories will provide the necessary instruction to enable these persons to perform useful national work.

The laboratories of our universities, university colleges, and technical institutions are at the disposal of the Government, and in many of them men are devoting twelve hours a day to work in connection with the supply of munitions of war. A few days ago the members of the Royal Institution decided to offer the resources of their laboratories and of the Davy Faraday Research Laboratory to the Government for the prosecution of any particular research by officers of the Admiralty, War Office, or Ministry of Munitions; and the managers invited communication from these departments "in case there is any field of research in relation to Or connected with chemical and physical science, or either of them, to which the professors, assistants, and staff of the Royal Institution or of the laboratory can usefully direct their attention with the view of giving assistance to his Majesty's Government in the conduct of the war."

We notice that this resolution was sent to the First Lord of the Admiralty, the Minister of War, the Minister of Munitions, and the chairman of the Inventions Board of the Admiralty, but we can scarcely suppose that each of these officers of State will act independently in making whatever use is possible of the offer. Mr. Lloyd George has announced in the House of Commons that he has made arrangements with the Secretary of State for War to take over the invention work relating to the munitions of war for the supply of which his department is responsible. He has also arranged with the First Lord of the Admiralty to take over the work relating to new expedients and inventions for purely Army purposes which are at present in charge of that department.

This action is in the direction of the establishment of the proposed central committee or bureau

to direct scientific and inventive energy into channels of effective work. In his recent address to the British Science Guild, Sir William Ramsay described Lord Sydenham's scheme for the constitution by the Royal Society of a general advisory committee to which all Departments of State would be directed to apply for assistance in problems requiring scientific treatment and investigation. The Royal Society is already in close association with the Government departments, and has instituted helpful work on many problems relating to the war, but there seems to be a need for common action between it and other scientific societies, both as regards the preparation of a joint register and the co-ordination of consultative committees. When such an organisation has been established, it should not be in separate connection with the Admiralty, War Office, Ministry of Munitions, and Board of Trade, but with a bureau to which scientific suggestions or inventions would be addressed, with the sure and certain knowledge that they would be submitted to expert trial and judgment. It is not yet clear whether Lord Fisher's Board is to be this central body or whether further committees are to be established by other Government departments concerned with scientific problems of the war and munitions. Good organisation demands concentration of effort upon common problems; and that end will not be reached by separate departments and separate scientific societies appointing their own committees and panels of consultants for independent work and advice. Co-ordination might be attained by the constitution of a grand committee on which each department and each scientific society concerning itself with national work would be represented, or a sort of official exchange might be established to which all suggestions or needs would be communicated, either to be dealt with by a small scientific staff attached to it or distributed to expert advisers for judgment. Only by linking up the various departments with one another and with scientific societies somewhat in this fashion can overlapping be avoided and the fullest advantage be secured most expeditiously from the services which men of science are prepared to place at the country's disposal.

Most people assume that these services will be voluntary; and a correspondent directs our attention to the fact that in the forms circulated by the Physical Society in connection with the proposed "War Register," it is stated that: "It is to be understood that all service would be voluntary, and unpaid, being given for the good of the country during this period of emergency." He adds: "I should like to inquire how it comes about that the Physical Society is not in a position to offer remuneration for work of the character specified in the circular on a scale at least bearing a reasonable proportion to the wages paid by the Government for the performance of less responsible labour. Is it really for the good of the country that this work should be unpaid?"

Government departments and statesmen find their requests for expert advice and guidance re

sponded to so willingly by scientific men and societies that they overlook the necessity of making any recompense for work done. In the medical services every qualified practitioner receives rank and reasonable pay, while consultants are given generous retaining fees. In legal circles also no advice is expected without a retainer is attached to it; and in this connection we are interested in the announcement that "according to a statement made in the House of Commons Sir John Simon, as Attorney-General, drew 18,000l. as his remuneration for the past year." It should be unnecessary to urge that the laws of nature are of as much importance as the laws of the land, and that as in the present crisis men of science can be of greater service to the nation than lawyers or politicians, they should receive at least sufficient reward for it to enable them to put aside their daily work in order to take up national duties. There will be no lack of volunteer workers among scientific men, but the State should understand that its responsibility for payment on account of expert opinion is at least as great in the case of science as it is in law, medicine, and engineering.

THE EVOLUTION OF THE
GONIOMETER.

THE
'HE goniometer-as the instrument used for
the measurement of the interfacial angles
of crystals is called-has gradually developed
from a simple and crude piece of apparatus to a
refined and somewhat complex optical instrument,
and the measurements made with it have become

increasingly more accurate as the form improved, while on the other hand the methods of investigating the morphological characters of crystals have on the whole become simpler. Nicolaus Steno, who (in 1669) was the first to study the angles between the plane surfaces of crystals, laboriously determined them by slicing the them by slicing the crystals perpendicular to the edges bounding the faces in question, and outlining the sections on paper. The first instrument used for the purpose of measuring the interfacial angles is that known as the contact-goniometer, and was devised by Carangeot in 1783; it is used to this day for measuring large rough crystals. This type consists essentially of two arms, one movable with respect to the other, which are laid on the faces in question at right angles to their common edge; the position on a graduated scale of the end of the movable arm beyond the pivot gives the angle required. A cheap form of this type made in cardboard or celluloid was designed by S. L. Penfield in 1900. Accuracy to single degrees of arc is the utmost that can under the most favourable conditions be expected of the contact-goniometer.

To the ingenuity of W. H. Wollaston, in 1809, is due the reflective form of goniometer. In this type the common edge of the pair of faces under measurement is set in line with the axis of a rotatable graduated circle, and the position of the circle is read when some distant signal is reflected by the particular face in a predetermined

direction; the circle is rotated, and the read taken corresponding to the second face. I difference betwen the pair of readings gives t interfacial angle required. In the original for the graduated circle was vertical, and no mean existed for fixing accurately the direction of ference. In a goniometer described shor afterwards, in 1810, by E. L. Malus, a telescope of low power was used for receiving the flections, and assuring, therefore, the constan of the direction of reference, and in 1839 Babinet designed an instrument with a horizon'a circle. E. Mitscherlich introduced many improve ments and accessories in 1843; he added a col· mator in place of a distant signal, and his screw arrangements for centring and adjusting th crystal are in principle the same as those general used now. The horizontal-circle form of gonmeter is extensively used at the present day, ar the optical features and accessories have bee brought to a high standard of perfection by the well-known firm of R. Fuess, of Berlin, who have devoted considerable attention to crystallographical instruments. Spider-lines were first used in the collimator, and afterwards the ordinar spectroscope-slit, but neither are satisfactory for goniometer work owing to the diffusion of the image on reflection at the tiny faces such as ofter occur on crystals. The difficulty was investigated by C. F. M. Websky, and in 1878 he described a slit, the jaws of which consisted of coplanar circular discs in contact, or nearly so, at the middle. This slit allows plenty of light to pass at the top and bottom, and the constriction at the centre admits of refined readings. In its origina form, or slightly modified, this slit is universally used in modern goniometers. For the purpose of viewing the crystal while in position and deter mining what face gives a particular reflection, the telescope is usually supplied with a lens which is applied in front of either the objective or the eyepiece for converting it into a microscope of low power. In a well-made instrument, if the crysta reflections admit, readings may be made to 30 minutes of arc.

Various modifications of this type have from time to time been devised. In 1903 H. A. Miers used an inverted form, that is one in which the crystal is suspended below the graduated circle, for making observations on crystals growing in their mother liquor. He also designed a stage goniometer for the measurement of the optic axia angle of small crystal flakes under the microscope. More recently, in 1911, Dr. A. Hutchin son designed a convenient form of inverted gonicmeter for the study and measurement of ti crystals or crystal fragments. In the univers goniometer (Fig. 1), as he terms it, the telescope A and collimator C are placed at some convenient angle to one another, and a microscope B is s arranged that its axis bisects the angle between them. The instrument may be used in t ordinary way as a goniometer, as an axial-anga apparatus (a fitting carrying nicol and condensing lens being placed for the purpose opposite microscope), as a total-reflectometer of the Kob

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