most of the species are only summarised briefly, greater space being allotted to those of commercial importance. Considerable attention is, of course, given to china-clay, and this chapter paves the way for an important one on pottery. Incidentally in these chapters many questions of scientific importance are discussed; for instance, solid solutions, mixed crystals, hydrated salts, and the classification of the silicates; Prof. Le Chatelier himself adopts in this book a chemical. classification. The admirable work done at the Geophysical Laboratory, Washington, on the artificial production of certain groups of silicates and the determination of their properties, receives adequate treatment. In the concluding chapter the author reviews very briefly the principal rocks and their classification, and the fluxes.

The book is well printed, but, like French books in general, is issued unbound and with uncut leaves. It unfortunately lacks an index.

NEW BOOKS ON CHEMISTRY. (1) Modern Steel Analysis. By J. A. Pickard. Pp. viii+128. (London: J. and A. Churchill, 1914.) Price 3s. 6d. net.

(2) The Synthetic Use of Metals in Organic Chemistry. By A. J. Hale. Pp. xi+169. (London: J. and A. Churchill, 1914.) Price 4s. 6d. net.

xii + 411.

(3) A Third-Year Course of Organic Chemistry. By Dr. T. P. Hilditch. Pp. (London: Methuen and Co., Ltd., n.d.) Price 6s.

(4) The Viscosity of Liquids. By Dr. A. E. Dunstan and F. B. Thole. Pp. vii+91. (London: Longmans, Green and Co., 1914.) Price 35. net.

(5) Intermetallic Compounds. By Dr. C. H. Desch. Pp. vi+ 116. (London: Longmans, vi+116. Green and Co., 1914.) Price 38. net. (6) De la Pirotechnia (1540). By V. Biringuccio. A Cura e con Introduzione di A. Mieli. Vol. i. Pp. lxxxv+ 198. (Bari: Società Tipografica Editrice Barese, 1914.) Price 3 lire.

(1) TH

HE little volume by J. A. Pickard is one which may be safely recommended to those who are engaged in iron and steel analysis. The introductory chapter might indeed be read with advantage by any analytical chemist whatever his speciality. The sodium bismuthate method for the estimation of manganese is fully described, and the volumetric methods for the estimation of phosphorus, nickel, and chromium, in short, the various processes, so far as the writer can judge, are well up-to-date. It may be observed that the author does not mention the

use of porcelain funnels or Gooch crucibles, but recommends pulp filters laid over perforated discs in ordinary funnels. It is impossible to say without experience what advantage the pulp filter has over well-fitting paper discs in a small Buchner funnel, but from the description the former seems the more troublesome arrangement. No reference is made to the moist combustion method described many years ago by Turner in which the carbon was filtered through asbestos and ignited sand contained in a hard glass tube and burnt in situ; for Turner's method seems more convenient and accurate than the process described here, involving the transference of the carbon and filter to the

combustion tube.

(2) The rapidly increasing use of metals in organic synthesis in recent years has expanded the literature to such dimensions that something in the form of a summary of the methods has become almost imperative, and it is a significant fact that books on the synthetic use of metals have appeared almost simultaneously in both German and English.

The small volume by A. J. Hale includes all the more important methods, which, though not described exhaustively, are thoroughly typical and sufficiently elaborated to render the various processes easily understood. References are also given to the original literature, so that the reader may always supplement his knowledge by turning to the original source. The plan of collecting them at the end of the chapters involves a certain inconvenience, for it necessitates constantly turning over pages, and, as the authors' names are omitted, one is occasionally left in ignorance of rather interesting, if not indispensable, information. The proper place for a reference is surely on the same page as the subject referred to.

It

(3) The volume on organic chemistry by Dr. Hilditch is the third and last of the series of text-books on this subject which have been prepared for the use of technical institutes. contains chapters on heterocyclic compounds, the purine group, polypeptides, carbohydrates, terpenes, and the alkaloids.

It would perhaps be more correct to call it a book of reference than a third-year text-book; for it is so closely packed with facts and formulæ that it would tax the powers of an exceptionally good memory to assimilate a fraction of the material in one year. It might also be added that the lettering of the formulæ, especially of the ring compounds, is a severe strain on the eyesight, and might be printed in larger type with great advantage. The book has, however, been carefully and thoughtfully compiled, and should prove useful not only to students of technical institutes

and university colleges, but to others who have an interest in the more intricate branches of organic chemistry.

(4) Among the more valuable of the series of monographs on inorganic and physical chemistry published under the editorship of Prof. Findlay is the volume on the viscosity of liquids, by Dunstan and Thole. The subject is, in a sense, in an elementary stage, but the foundations have been laid, and the results, which have been obtained by the authors who may be looked upon as pioneers in this branch of physical chemistry, promise a valuable aid in elucidating many interesting problems. As the authors state in the preface, the additive effect of a physical property is of little use for the purpose of studying structure; but viscosity, like optical rotatory power, is mainly constitutive, and the difficulty in both cases lies in the interpretation of the numerical values.

The various chapters describe the apparatus, methods of measurement and of calculation, the measurement of the viscosity of pure liquids, of mixed liquids, of electrolytic solutions, colloidal solutions; and the final chapters are devoted to discussing the relation of viscosity to chemical constitution.

It is impossible in the short space allotted to this review to discuss the results; but the volume is a unique contribution to chemical literature, and well worth reading.

(5) The monograph on intermetallic compounds, by Dr. C. H. Desch, has reference to those mixtures of metals which form true compounds, and the methods by which such compounds may be distinguished from simple alloys. That the subject is an intricate one may be judged from the numerous erroneous results which marked the first attempts in this direction, and by the not altogether satisfactory character of the present available data. The first accurate investigations were made by Heycock and Neville in 1897 by means of the freezing-point curve, and these have been followed more recently by the work of Tammann and his pupils. That the subject has been very widely studied may be seen by the long list of references, more than 200 in number, which are given at the end of the volume. The chapters are divided into the following subjects: thermal analysis, microscopic structure, the isolation of intermetallic compounds, their physical properties and chemical nature. The subject is one of the first importance to metallurgists, to whom this excellent and complete summary should make a special appeal.

(6) "De la Pirotechnia," of Biringuccio, of which the present volume is a reprint, appeared in

1540, the year following the death of its author. It has been edited and annotated by A. Mieli, who has also added a valuable introductory and biographical notice. As the name of Vannoccio Biringuccio is little known to English students of chemical history, it may be stated that he was born at Siena in 1480 and died in 1539. His father was an architect, but the son devoted his attention chiefly to metallurgy and mining, and paid several visits to Germany and Austria and other countries in pursuit of his studies. In the disturbed state of Italy at this period, when the Italian towns were constantly in conflict, the fortunes of those who allied themselves with the ruling families were apt to suffer. It is not surprising to find that Biringuccio was twice banished from his native city, when his patrons, the Petrucci, got into hot water, and was also twice recalled.

He was a contemporary of George Bauer (Agricola), whose great work on mining and metallurgy, “De Re Metallica," appeared a little later; for in it a reference is made to Biringuccio, in which Agricola recognises the debt he owes to the work of his predecessor.

Mieli, in his introduction, comparing the work of Agricola with that of Biringuccio, says:

"In Agricola we have the mineralogist and metallurgist, and in certain respects the geologist. Agricola was a man of much erudition, and his work is full of classical references. But BirinNot only do many

guccio was something more. portions of the book attest a profound knowledge of chemistry; but they reveal the artist, the craftsman, and the inventor. If Agricola has observed and described, Biringuccio has manufactured and invented new methods and machines, and shown his artistic temperament in the production alike of big and little things. He could cast a cannon as well as a church bell."

OUR BOOKshelf.

Memorials of Henry Forbes Julian. Written and edited by his wife, Hester Julian. Pp. xix+310. (London: C. Griffin and Co., Ltd., 1914.) Price 6s. net.

HENRY FORBES JULIAN, sprung from a Scoto-Irish family, was born at Cork in 1861. During his childhood his family migrated to Bolton, in Lancashire, and there his taste for scientific research was aroused under the teaching of Sir Henry Roscoe at Owens College, Manchester. He began his life as a metallurgist and mining engineer in South Africa, where he did much falls of the Zambezi. exploring in the Barotse country, and visited the He devoted himself to developing the cyanide process of ore reduction, and in collaboration with Mr. E. Smart wrote a standard treatise, "Cyaniding Gold and Silver

Ores." In 1894 he carried out further research on behalf of the Frankfurt Gold und Silber Scheide-Anstalt, and as a consulting metallurgist made repeated voyages to Mexico and other parts of the American continent.

Mr. Julian was a man of wide scientific knowledge, a constant attendant at meetings of the British Association, and other scientific societies, and he had acquired a wide knowledge of literature. A modest, cheerful man, he made hosts of friends, and after his marriage to a daughter of William Pengelly, the well-known geologist and explorer of Kent's Cavern, his home at Torquay became the centre of much scientific and literary activity. On his last voyage to America, on work connected with a patent case, he perished in the wreck of the Titanic. Though few details of this final tragedy are available, he certainly displayed the heroism and unselfishness which were the leading characteristics of his life.

In the present memoir compiled by his widow the material is thin, and some of the less important incidents of his life are described with more detail than is necessary. But in the circumstances this is excusable, and the memoir gives a vivid sketch of a life devoted to the cause of science and of an amiable and attractive personality.

A Practical Handbook of the Tropical Diseases of Asia and Africa. By Dr. H. C. Lambart. Pp. xv+324+ plates. (London: C. Griffin and Co., Ltd., 1914.) Price 8s. 6d. net.

We are told in the preface that "the intention of the author has been to show at a glance, by its alphabetical arrangement, the diagnosis and treatment of the principal tropical diseases; the subjects treated will be found stripped to essentials, and the pages nowhere encumbered with disputed points or theories still sub judice, the book thus being arranged for readiest reference."

Such works are seldom to be recommended, because they involve too brief and fragmentary a treatment of subjects which must be dealt with thoroughly if they are to be understood at all; and they are to be recommended still less in medical matters, which are concerned with the life or death of patients. Medical men in the tropics have enough time at their disposal to read at least much fuller text-books than this one, which is apparently designed for the most cursory of readers. Thus, the vastly important clinical theme of abscess of the liver, requiring the utmost care in diagnosis and in medical and surgical treatment, is dealt with in three pages (without mention of Rogers's emetin treatment); and the junior medical man who would trust to this brief note alone might go very seriously wrong.

The author, moreover, can scarcely be commended, for the carefulness of his abstracts, or for his grammar, his drawings, or, indeed, his general design, and the accuracy of many of his statements is open to question. The whole work suggests a compilation taken down from previous text-books or from lecture-notes; and the number of similar books on the same subject is aiready too large.

Leitfaden für Aquarien- und Terrarien-Freunde. By Dr. E. Zernecke. 4, ganzlich neu bearbeitete Auflage von C. Heller und P. Ulmer. Pp. vii+456. (Leipzig: Quelle and Meyer, 1913.) Price 7 marks.

DR. ZERNECKE'S handbook for the amateur management of aquaria and the like is full of valuable information. It pays sufficient attention to amphibia, lizards, snakes, and such small deer, and it touches on the salt-water aquarium, but its full strength is concentrated on the popular fresh-water aquarium. Full directions are given for the installation, aeration, sanitation, and general maintenance of this humanising educational instrument, and a host of water-plants, fishes-both native and exotic-and invertebrates of all kinds are introduced with suitable credentials and attractive portraits.

The Continents and Their People: Africa, a Supplementary Geography By J. F. and A. H. Chamberlain. Pp. vii+210. (New York: The Macmillan Co. London: Macmillan and Co., Ltd., 1914.) Price 38.

THIS book provides an account of Africa and its people which serves to supplement the more technical descriptions of the text-book. Opportunity is taken to give a full treatment of the industries dependent on dates and diamonds. The nomenclature of the States should have been brought up to date, and the account of the causes of the Nile flood should be revised.

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 Determination of Sex in the Gall-fly, "Neuroterus lenticularis " ("Spathegaster baccarum ").

It is well-known that many Cynipid gall-flies of the genus Neuroterus (Spathegaster) have two generations in the year, one generation of parthenogenetic females and a second generation of males and sexual females. I have previously shown (Proc. Roy. B lxxxii.,

p.

1910, p. 88, and B lxxxiii.,

Soc., 1911,

476) that any individual parthenogenetic female has either only male or only female offspring, and that the eggs of the male-producers undergo maturation of a different type from those of the female-producers. I suggested that possibly the determination of male-producing or female-producing individuals depended on the existence of two kinds of spermatozoa. Further experiments extending over the last two years have shown that this suggestion is mistaken, and that the difference between the maleproducing and female-producing parthenogenetic females is derived from the sexual female parent. It will take several months at least to complete the cytological investigation of the phenomena which I have in hand, and therefore it may be of interest shortly to record at once the results of the breeding experiments, for they show a type of sex-determination not previously known in the Hymenoptera.

The experiments indicate that any individual sexual female produces either only male-producing or only female-producing parthenogenetic offspring, but not both. Individual fertilised females were allowed to lay on sleeved oak-leaves in May, 1913; the galls produced by each were collected, and sleeved on oak leaves in March of this year. On examining the flies produced, I found that, with a few possible exceptions, the grandchildren of any one sexual female are either all males or all females. I have examined more than 9000 grandchildren of the twelve fertilised females sleeved in May, 1913, and among these there are about 2 per cent. of exceptions to the rule that all the grandchildren of any sexual female are of the same sex. The exceptions, however, do not occur in all the sleeves, but in rather less than half, and I have little doubt that they are due to wild flies having been able to lay eggs in the buds through the muslin of the sleeves. The wild flies were exceptionally abundant this spring, and it is difficult to prevent the buds from pressing against the muslin in such a way that a fly on the outside could not lay in them. I intend to test this possibility next spring, but meanwhile the results obtained make it certain that nearly, if not quite all, the grandchildren of any sexual female are of one sex, and that of the sexual females, those which have male or female grandchildren are about equally L. DONCASTER.

numerous.

Cambridge, September 21.

anti-kathode (Fig. 3.). Around this axis the effects are increasingly asymmetric. This is shown by the variation of the white band (from a full circle to nearly a semi-circle) within the shadow, and of a dark area between it and the boundary of the image. The positions of maximum intensity have been determined by the photographic and electroscopic methods (see NATURE, August 13, Röntgen Journal, July and October, 1914), and are found to be always directed to the optimum axis. The asymmetry has also been established with V-apertures and squares of metal, where the white band appears on one, two, or three (asymmetric), or four sides (symmetry) according to the relative positions (70° to 0°) to the axis of symmetry. The bulb must, of course, be rotated on the spot as centre. In addition to these effects, already described, we have now ascertained that the "diffracted" rays are almost entirely re-diffracted by a second edge. The re-diffraction (as in the case of primary diffraction probably) occurs in two directions, i.e. within and without the shadow. Moreover, these effects are again definitely asymmetric when other than optimum rays are used. For instance, a lead disc perforated by apertures symmetrically arranged is shielded by a solid disc of slightly larger dimensions to secure that no rays except those already diffracted by it can reach the second disc. The perforated disc may be placed 0.7 cm. from the plate, and 19 cm. from the anti-kathode, 2.7 cm. separating the discs.

Asymmetric "Diffraction" and "Re-Diffraction" of X-Radiation.

FURTHER work upon this subject, briefly described in previous letters (see NATURE, July 16, p. 507), has shown that for any one position of the bulb and object the angle of diffraction is constant. This angle, however, varies with the distance of the object from the source in accordance with a simple inverse sinelaw (sin x dcm=7.5), over the wide range of 8° to 40°, and 50 to 10 cm. This and other well-marked differences from light have been already noticed in our previous papers, and a table of the sine values is given in the present (October) number of the Röntgen Journal.

FIG. 3.-Map of hemisphere of X-rays (lead disc) showing radial structure radiation. Reduced 4 diameters.

These rays, being normal to the disc, and leaving the anti-kathode at any other than the optimum angle, the images of the perforations will be seen (Figs. 1 and 2) to be increasingly displaced, distorted, and altogether absent in the extreme position. The asymmetry is marked at opposite points, and not at the ends of rectangular axes as would be the case were the phenomenon one of ordinary polarisation.

A black band outside the shadow is naturally only observed when the rays are thus shielded, for otherwise it falls in the area of undiffracted direct radiation.

In these experiments especial care has been taken to keep the milliamperage constant between 1 and 1.5, by means of a variable resistance in the primary. I. G. RANKIN.

W. F. D. CHAMBERS.

GLASS FOR OPTICAL PURPOSES.

THE

HE importance of an adequate supply of optical glass of all the principal types cannot be overestimated. The improvement of the microscope has been and is still retarded for the want of suitable glasses, the construction of large telescopes is limited by the capacity of the glassmaker to supply suitable discs of glass, and the improvements made in the design of small telescopes cannot be extended to larger sizes for the want of suitable glass.

Photographic lenses, binoculars, range-finders, and telescopes of all kinds are dependent for their performance on the good quality, both optically and physically, of the glass used in them. The The magnitude of this special branch of the glassmaking industry may be gauged from the value of the German exports. In the last year for which figures are available the value of the exports of unworked optical glass exceeded fifty thousand pounds, and large quantities were exported as finished lenses. The characteristic of optical, as distinguished from other glass, is its great homogeneity; veins of material of different composition even in the form of very fine striæ render glass unsuitable for the better class of optical work.

The history of optical glass-making is to a large extent the history of optical progress. Dollond's discovery of the achromatic combination (1757) created a demand for flint glass suitable for optical purposes. At first this demand was met by the selection of the most suitable pieces from the glass manufactured for other purposes, but the demand for larger discs of flint glass led Guinand (1748-1824) to work out new methods of melting flint glass. The essential feature of his method was the continual stirring of the glass to prevent the formation of striæ of different density. Guinand migrated from Switzerland to Bavaria, and in conjunction, first with Utschneider and later with Fraunhofer, improved the process, so that larger blocks of good uniform glass could be manufactured regularly. On Guinand's return to Switzerland, Fraunhofer continued his experiments, and was able subsequently to make good discs of flint glass up to 10 in. in diameter. Meanwhile Guinand had increased the size of discs up to 14 in. diameter, and on his death in 1824 the secret passed to his sons, and through them to Bontemps in France. Bontemps' work was carried on by the French house of Feil, now Parra-Mantois, while Bontemps himself brought the secret process, in 1848, to the glass-works of Messrs. Chance.

For some time the principal advance was in the improvement of the physical properties of the glass, greater uniformity, greater transparency and more durability being aimed at. The calculation of the Petzval portrait lens and its successors led to a large demand for a glass intermediate in type between the ordinary flint and the crown. For this purpose, and for use in the other types of photographic lenses, the series of light flints was worked out. In this series the percentage of

lead oxide increases as a higher refractive index is required.

The progress of the microscope makers required the extension of this series of glasses to denser flints, i.e. glasses of higher refractive index; at the same time small variations in the constitution of the crown glass were made to give slightly differing optical properties. In this way, by the year 1880 it was possible to make a complete series of glasses with their refractive indices ranging from 1515 to 172. But these glasses had two special characteristics: as the refractive index increased, the dispersion, i.e. the difference in the refractive indices for light of two chosen colours, increased more rapidly, so that it was always necessary to use the glass of lower refractive index for the positive lens of an achromatic combination; also the dispersions of two glasses. of different refractive index were not proportional throughout the spectrum, so that if a combination of a crown and a flint lens were made to bring the red light proceeding from an object to the same focus as the blue light, the yellow and violet light would not come to the same focus. The consequence was that all images appeared coloured, in spite of the choice of the most suitable curves for the two lenses; this defect is termed "secondary spectrum."

Many attempts had been made to obtain a pair of glasses which would enable the lens-maker to get rid of this secondary spectrum. The experiments of the Rev. W. V. Harcourt (1789-1871), which extended from 1834 to 1871, showed that this problem could be solved; he proved that the effect of substituting boric acid for part of the silica in the glass was to reduce the dispersion of the blue end of the spectrum, and so to make a flint glass which more nearly matched the ordinary crown glass. He was also able to modify the crown glass by using phosphoric acid, but wrongly attributed the result to the presence of titanic acid. Unfortunately these experiments did not lead to practical results, probably because of the expense attaching to experimental meltings on a practical scale.

The next stage in the development of optical glass was the investigation by Schott and Abbe (1881-1886) of the effects of using different materials. With consummate experimental skill, and assisted by generous grants from the Prussian Government, they were able to determine the effects of employing different materials. They were able to confirm Harcourt's results as to the action of boric acid, and correctly to attribute the effects observed by him to phosphoric acid. In addition, they were able to determine the effects of barium both with and without boric acid.

Now the use of boric acid in the ordinary lead glasses always leads to a glass which is more or less liable to spot, but by the use of barium instead of some of the lead this effect is reduced. The boric acid barium glass is, however, of special value, because in this case a high refractive index is associated with a low dispersion. It behaves as a crown glass as regards its dispersion, but