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THURSDAY, SEPTEMBER 16, 1909.

PRINCIPLES OF IGNEOUS PETROLOGY. The Natural History of Igneous Rocks. By A. Harker, F.R.S. Pp. xvi+384. (London: Methuen, 1909.) Price 12s. 6d. net.

FOR

'OR some time the need of a text-book of general petrology in English has been acutely felt, owing to the rapid progress which the science has made in theoretical subjects and the inaccessibility of many of the original memoirs to students and teachers. Most text-books treat the subject from a purely descriptive point of view, and the speculative developments are kept in the background. In fact the literature of descriptive petrology is now so large that an attempt to extract the general conclusions to be deduced from the observations becomes of greater importance than merely to add to the number of ascertained facts. In a book of about four hundred pages Mr. Harker endeavours to meet this demand, and has covered so wide a range and compressed so much information into this brief space that he has achieved a very large measure of success.

The work is confined to the investigation of the principles of igneous petrology, and the metamorphic and sedimentary rocks are excluded from its scope. The title fairly expresses the aims of the book; it is an attempt to treat of igneous rocks in the manner of natural history, taking account not only of their minute anatomy and structure, but also of their distribution, their range in time, and their genetic associations. Of late years there has been a plethora of unnatural systems of petrology, based on purely arbitrary lines. On the best known of these (the "quantitative classification ") the author passes severe judgment, and returns to the broader treatment followed by Rosenbusch, Brögger, Judd, and Teall. That combination of geological reasoning with petrological analysis which has always characterised the English school of petrologists finds able expression in the pages of this treatise.

The geographical distribution of recent volcanic rocks is considered in the introductory chapters, and the remarkable association of "Atlantic and "Pacific" rock types with certain classes of tectonic developments is made the foundation of an appeal for a natural classification. Undoubtedly the facts are most impressive, though we are entirely in the dark regarding their causes; and they afford the clearest indication that in time we shall be in possession of natural systems of petrography. We learn incidentally that the first sketch of this grouping was presented by Mr. Harker, though it has become more generally known through the treatment of Dr. Prior and Prof. Becke. The Tertiary volcanic rocks of the Inner Hebrides are placed among the Pacific types, a conclusion by no means easy to accept, and one which may need to be revised at some future date.

The application of physical chemistry to the crystallisation of magmas is taken up in considerable detail. This part of the book is practically a summary of Prof. Vogt's papers, and leaves nothing to be desired

in lucidity of exposition and accuracy of statement. For students it will be of the greatest value, as the original memoirs are loaded with detail, and much too voluminous for their use, and no satisfactory account of them has hitherto appeared in English. We must confess, however, to a certain feeling of disappointment in reading them, a sense of incompleteness. The a priori principles are laid down in a very satisfactory fashion, but the applicability of these principles to the actual concrete facts of rock structure and history, which we had a right to expect from a geologist of Mr. Harker's wide experience, is dismissed with scant treatment. The difficulty of interpreting the history of crystallisation in the commonest rocks in terms of the theoretical principles laid down is sure to face the student at an early stage in his studies. We miss in particular any reference to the work of Schreinemaker, who has proved by analytical investigations that in a solution of three minerals in one another, of which two can form mixed crystals, while the third is independent, there are many possible schemes of crystallisation; one mineral may separate out completely at an early stage, and the crystallisation of any substance may be interrupted or repeated, If there are more components, or if we allow for the influence of dissolved gases in the magma, the problem becomes much more complicated; but it is a relief to find that as the theory is better understood the discrepancies between it and the observed facts seem to diminish.

The subject of "hybridism," or mixed rocks, is discussed in a brief chapter, which sums up in admirable fashion the results of the author's work in this difficult field. He takes a middle position between the schools of petrology which deny that igneous rocks dissolve sediments or older rocks with which they come into contact, and those which hold that such processes go on on a large scale, and that many rocks generally regarded as of normal types are thus produced. Mr. Harker's field work enables him to speak on this subject with great authority, and his conclusions are so moderate and so firmly based on sound evidence that he carries us with him in all that he says. There is also a chapter on magmatic differentiation, a subject on which it does not seem possible to say anything that is new, and a very interesting account of the mutual relations of associated igneous rocks which, in our opinion, is the best in the volume. The curves drawn on a very simple graphic system show the variation in the components of allied rock types, and are convincing that some general principles must underlie the facts, though as yet we have been unable to grasp them. The final chapter on classification is unexpectedly brief, and contains an admission that existing systems are merely temporary stop-gaps, and a satisfactory classification must traverse the lines of all current groupings, and will require an entirely new nomenclature. To us this appears unduly pessimistic, and we believe rather that in petrology as in other sciences the future will be the child of the past, and that real progress will not involve the demolition of the older systems, but will include them while giving them a

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CHE favourable opinion we formed of Mr. Finn's work when the first part was noticed last year in NATURE we are pleased to be able to endorse now that the complete volume is before us. The book is confessedly a thoroughly popular one, and, therefore, ought to be judged solely from that standard; and from that point of view it may be pronounced a decided success. The author's style of writing is bright | and attractive; and in the main his descriptions appear correct and up to date. Mr. Finn has not overloaded his text with names of naturalists and observers about whom the public knows little or nothing; and he has, in our opinion for the most part rightly, altogether ignored subspecies. As regards nomenclature, the author will have nothing to do with modern innovations and changes, and we accordingly find the baboons (and not the flyinglemur) appearing under their old title of Cynocephalus, and the fox as Canis vulpes. The fact that such names still dominate in popular literature suggests that they. should not, as is now too much the fashion, be ignored in our museums, which are primarily popular institutions.

Mr. Finn appears to take as his texts the hundred mammals represented in the coloured plates, as the descriptions of all these are printed in larger type 'than is conceded to many of the others noticed. Personally we are not enamoured of this plan, as it suggests that the species to which large type is accorded are of more importance than the rest; but this point is not one affecting the character of the work as a whole.

The coloured plates form, of course, the characteristic of the volume which will appeal most strongly to the general public; and for these illustrations-the only ones in the book-we have in the main nothing but commendation, although some appear rather too brilliantly coloured. A few, moreover, do not indicate important details-notably the one of the hamster, in which the dorsal gland-patch is not shown. The one serious error in the illustrations occurs in part xii., where the plate lettered Marco Polo's wild sheep really represents the true argali (Ovis ammon); and there is no excuse for this, as the figures, if we mistake not, have been drawn from the mounted specimens in the British Museum. Nor is this all, for, whereas the figure in the foreground depicts, as we have said, the true Altai argali, the one in the middle distance is taken from its Tian Shan representative. In the concluding part we notice that the plate of the platypus shows the web

of the forefoot fully extended when the animal is on land, in place of being folded beneath the palm, as it must be in order that the creature should get a foothold.

Misprints and other errors in the text appear to be few, but we notice on p. 47 Mipsiprymnus for hypsiprymnus. In the account of the Derbian eland no mention is made of the fact that the species occurs in the Bahr el Ghazal; while the occurrence of the water-chevrotain in East Central Africa is ignored. The old error as to female takin-horns differing in form from those of the male is also repeated.

Most of these are, however, but trifling errors, which detract but little from a work worthy in the main of high praise. R. L.

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(1) THIS

HIS book is intended to be a text-book for engineering students during the first year of their course, and the examples selected to illustrate the principles discussed are, therefore, mainly such as are likely to be met with in practical engineering work. To facilitate the working out of the numerical problems, of which there are nearly 300 scattered through the book, the author has printed in the form of five appendices a series of tables including hyperbolic functions, logarithms of numbers, trigonometrical functions, squares, cubes, square roots, conversion tables, &c. ; it is very problematic as to how often such tables incorporated in a text-book are of use to the student-it is much more convenient for him to have a small thin book of mathematical tables, and there are several such books now available, which he can carry about with him in his pocket, and refer to whenever calculations have to be made.

Two very complete chapters are those devoted to centre of gravity and moment of inertia; the application of Simpson's rule to the finding of the area and centre of gravity of rail and similar sections is fully discussed, and the whole subject of the determination of moments of inertia of various standard sections is treated very fully, both by analytical and graphical methods: this is a matter of considerable interest to engineers engaged in structural design work. Another chapter which will be found of use by the engineer in practice as well as by the young student is that dealing with the dynamics of machinery: after dealing with such usual problems as those of the flywheel and connecting-rod in a reciprocating engine, a number of sections is devoted to the gyroscope, and to its application to the mono-rail and similar devices.

The last chapter in the book treats of impact in a

more satisfactory manner than is usually the case in text-books on mechanics. The book is certain to prove a useful one to all those who are engaged in teaching the subject of mechanics to engineering students, and the number of well-selected examples makes it a particularly satisfactory book for the student himself. Many young engineers are far away from help in matters of this nature, and have to depend upon their own resources-it is essential in such a case that they should have a large number of practical problems to work through in order to familiarise themselves with the principles underlying each branch of the subject.

(2) This book has been written specially for artillery officers detailed for duty in ordnance factories; it is copiously illustrated, and special attention has been given to the relative advantages and disadvantages of different types of machine tools, and to different methods of transmitting motion to the tools.

The first section is devoted to such details as the transmission of motion from one shaft to another by belting and gearing, quick return motions, cams, sliding pairs, turning pairs, and screw pairs, and in each case brief notes are given as to the important points to which attention should be paid in order to secure good results and to maintain all working parts in good order.

The second section deals with all the more impor

tant machine tools which are to be found in a modern workshop; in each case a regular order of treatment is followed-first the parts exterior to the machine itself and transmitting motion to it are discussed, and then in order the links in the machine receiving this motion, the links of the machine transmitting movement to the work, the links of the machine transmitting movement to the cutting tool, and lastly any other specialised link, and the frame. This is a method of treatment suitable not only for the nontechnical student, but also for students who are just beginning the study of machines and machine tools, and the illustrations, which form a special feature of the book, are so arranged that the reader has no difficulty in finding at once in any of the figures the link of the machine which is described in any particular paragraph of the written description of the machine.

The third section deals with the cutting tools used in the various types of machine tools, methods of tempering, angles for the cutting edge for different classes of work, methods of lubrication, and speed of cutting are all discussed in detail, and a few paragraphs are devoted to the employment of the new high-speed steels.

In view of the fact that interchangeability of parts is now so important in all cases where large numbers of similar machines are constructed, the fourth section is entirely given up to an account of the construction and use of various types of gauges, with a series of useful notes on the precautions which must be adopted to ensure that their employment shall secure the desired result. The book should be consulted by all those who are engaged in the design of machine tools. T. H. B.

A BELGIAN BOTANIST.

Notice sur Léo Errera. By L. Fredericq and J.
Massart. Pp. 153. (Bruxelles: H. Lamertin;
London Williams and Norgate, 1908.)
Recueil d'Euvres de Léo Errera. Vols. i. and ii.
Botanique générale. Pp. iv+318 and v+341. Vol.
iii. Mélanges Vers et Prose. Pp. xiv + 222.
(Bruxelles: H. Lamertin; London: Williams and
Norgate, 1908–9.)

are

T would be difficult to overestimate the influence IT of the two great German professors, Anton De Bary and Julius Sachs, on the progress of botany. At a time when many fundamental ideas were only beginning to take shape, these advanced workers and leaders of thought attracted a succession of brilliant students from many European countries, countries, who absorbed in Strassburg and Würzburg the doctrines and inspirations of their masters, and eventually spread abroad the new theories and conceptions that now regarded as the foundations of botanical science. Amongst this band of eager students was the Belgian, Léo Errera, who entered first De Bary's laboratory in 1897, and subsequently sought further experience under the tutelage of Sachs. Two important results can be traced to these courses of foreign study. In the first place, intercourse with such gifted teachers and with brilliant colleagues helped to stimulate the energies of an already keen enthusiast, and to pave the way for future friendships and associations. In the second place, his interests were diverted from systematic to chemico-physiological botany, which became one of the chief lines of research at the University of Brussels.

The first of his primary contributions to science was the paper on glycogen in the Mucorineæ; this was the outcome of research in De Bary and HoppeSeyler's laboratories, and required a profound knowledge of the two sciences of botany and chemistry. It was followed by other papers on the same and other physiological subjects published by himself or his students. Prof. Errera was also well yersed in mathematics and physics, evidence of which is furnished by the course of molecular physiology prepared for his advanced students. The researches connected with glycogen and the localisation of alkaloids, the papers on the application of physical chemistry to the elementary phenomena of cells, the relations of flowers and insects, and the defensive structures of plants, may be regarded as his chief contributions to botany.

As a professor, Errera took the keenest interest in his students, and spared no pains to stimulate their energies towards the acquirement of knowledge and the prosecution of research. At the time when practical courses were not yet customary he initiated a course which was first held in two small rooms in the gardens, and later in a more spacious laboratory provided at his own expense in a neighbouring building. The biography compiled by two of his former students bears testimony to the enthusiasm he inspired, and provides a realistic picture of his varied talents. He was an accomplished linguist, an excellent lecturer, and an entertaining companion.

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The papers on general botany collected in the two volumes noted above are of a popular nature, as his more technical contributions have been published in the Recueil de l'Institut botanique de l'Université de Bruxelles. The first is a letter describing the vegetation in the neighbourhood of Nice, written when he was sixteen years old. The article on the structure and methods of fertilisation of flowers appeared four years later; it was inspired by Charles Darwin's work, and the introductory quotation from the "Origin of Species," taken in conjunction with his essay on Darwinism, is worth reproducing Whoever is led to believe that species are mutable will do good service by conscientiously expressing his convictions." The article is, to a large extent, an account of contemporary investigation, but includes original notes on the oxlip and the genus Pentstemon. The essay entitled "Une Leçon élémentaire sur le Darwinisme" was revised in 1903, after the publication of de Vries's book. Errera fully accepts the mutation theory, regarding it as an amplification, and not a contradiction, of the selection theory. The references in this paper to Dr. Scott's work on Cheirostrobus and the joint communication by Drs. Scott and Oliver on Lagenostoma will serve to indicate how the author incorporated the very latest results into his teaching.

The most interesting part of the third volume, containing miscellaneous verse and prose, will be found in the collection of extracts and aphorisms. Here is an epigram that will be appreciated by philosophers generally :-" La vérité est sur une courbe dont notre ésprit suit eternellement l'asymptote." The authors of the biography are to be congratulated on presenting such an interesting account of the brilliant alumnus of Brussels University. The papers are worthy of consultation, not alone for the facts contained, but also for style and arrangement.

OUR BOOK SHELF.

An Atlas of Skiagrams, illustrating the Development of the Teeth, with Explanatory Text. By Dr. J. Symington, F.R.S., and Dr. J. C. Rankin. Pp. 47; pl. xii. (London: Longmans, Green and Co., 1908.) Price 10s. 6d. net.

THE difficulty of cutting sections comprising both soft and highly calcified parts without causing displacements, and the further trouble of piecing together the disposition of parts in a large number of serial sections so as to reconstruct a model in the solid, gives to skiagrams an especial value, as being a representation of the relations of the developing teeth to one another and to the jaws which is beyond suspicion of disturbance. Certain difficulties arising from the teeth being disposed in an arch were very successfully met by the authors, who resorted to tipping the back of the skull upwards to a uniform extent in all cases, namely, raising the back about 30 degrees, and by this method the shadows of the front teeth were separately projected and the overlapping of the shadows to a great extent avoided. The skulls used were divided into halves, and the right and left sides both presented in nearly every case where the skulls used were more than seven years of age; but in the younger ones, no difference being found between the two sides, only one is presented.

The ages of the subjects used range from birth to adult life, and twenty-three skiagrams are given which

illustrate the calcification of the temporary teeth and their change to the successional set; amongst other points clearly shown, the extent of calcification in each tooth, at each age, a point sometimes of medicolegal importance, is well seen. Some points in the relation of the growth of the jaws to the development of the teeth can be advantageously studied in these skiagrams, as well as the relation of the developing teeth to the antrum. Inasmuch, however, as the walls of the antrum cannot always be very clearly traced in the midst of shadows cast by other parts of the upper jaws, the anatomy of the antrum is also illustrated by drawings made subsequently from the same specimens, the technique adopted being to harden the tissues in formol, and then to chip away as much of the bone as could be removed without destroying all support. The lining membrane so treated becomes sufficiently firm to stand alone and retain its shape, and the dissections made were carefully drawn. These figures include also the accessory sinuses. The authors may be congratulated upon having produced an atlas which is of the greatest service in adding to the accuracy of our knowledge of the development of the teeth and of their relations to the parts about

them.

Mineralogie und Geologie für schweizerische Mittelschulen. By Dr. Hans Frey. Dritte Auflage. Pp. iv+234. (Vienna: F. Tempsky; Leipzig: G. Freytag, 1909.) Price 2.75 marks. THIS work, which has evidently been successful, is of the type commonly used in German-speaking schools, and makes no special appeal to the beginner's interest in field-observation, or to the splendid objectlessons ranged around him in his native land of Switzerland. A number of Swiss illustrations are, however, inserted, and the passages on mountainbuilding and the Alpine lakes embody considerations raised in recent times. To a British mind the mineralogical section will seem to contain far too much in a small compass, if the course is to be gone through systematically before the pupil enters on his collegiate years. It occupies half the book, and is followed by a petrographic chapter, which similarly bears traces of having been brought somewhat hesitatingly towards modern modes of statement and classification.

The section on historical geology, perhaps in accordance with a settled syllabus, is limited to thirty-four pages, and the illustrations of fossils are given without any explanation as to the nature of the organisms. In these circumstances, the generic and specific names are worse than useless; they need, moreover, some revision and press correction. A great opportunity still remains for making the mineralogy and geology of Switzerland serve as an introduction to these sciences, and for letting the land itself speak to the pupil, before he becomes entangled in the strings of facts which are supposed to be inseparable from a scientific education. G. A. J. C.

Gilbert White and Selborne. By Henry C. Shelley. Illustrated from photographs by the author. Pp. xvi+226. (London: T. Werner Laurie, 1909.) Price 6s. net.

THIS little book is not badly done so far as it goes, but there is nothing in it that has not often been said before; the photographs are good, but of quite familiar objects. The one innovation consists in eking out a volume offered at six shillings by "Cameos from the Natural History of Selborne," which occupy fifty of these meagre pages: a serious literary blunder, to use a mild word. The six shillings might be much better spent in the purchase of an edition of the famous book, which is much talked of but probably little read.

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 Summer Season of 1909.

IN endeavouring to estimate the character of a coming season, the following method is, I think, often serviceable. Let us take, as a concrete case, the annual numbers of very hot days at Greenwich (80° or more) from 1841 to 1908. Add these in the thirty years ending 1870, 1871, 1872, &c. Then compare each sum with the next by the dot method; where each dot represents one value by the horizontal scale, and the next by the vertical. A line may be drawn connecting points of intersection of lines (horizontal and vertical) from equal numbers in the two scales, and two others roughly parallel with it (as shown).

Now the last value, previous to this summer-the sum, that is, of the thirty years ending 1908-is 417. Find this in the horizontal scale, and consider where the next dot is likely to go. It would hardly be higher than (say) the level of 433. Now we know the numbers of those days in twenty-nine out of the thirty summers ending 1909; their sum is 416. Deducting 416 from 433 leaves 17; and we infer that this season would probably not have more than seventeen of those hot days (which is only two more than the average). The season has, so far, proved a very cool one (August 4). This method is obviously capable of wide application.

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so called) to the present season, following on a Rothesay year, which would fall to be added to the above list.

Once more; the summer season of 1879 is well remembered as a singularly cold one. There were only thirty days with 70° or more, and one with 80° or more (the averages being 77 and 15 respectively); and now, at thirty years' interval, we have another very cold summer.

Suppose we compare each summer with the thirtieth after, in respect of those very hot days (80° or more). We can carry the comparison obviously up to 1878 (that year compared with 1908).

It would appcar that, in the case of very cold and very warm summers, there is some tendency for the thirtieth after to be of like sign in relation to the average.

Thus the six coldest, in ascending order (o to 6 hot days), are 1860, 1862, 1841, 1853, 1855, 1845; in each case but one the thirtieth season after was cold, and that one was average. The six hottest, in descending order (40 to 27 hot days), are 1868, 1857, 1859, 1846, 1876, 1870; in each case but one (again average) the thirtieth season after was hot. The season of 1909 seems likely to conform to this. ALEX. B. MACDOWALL.

those very hot days (three in May, six in August), which P.S. (September 13).-There have been, so far, nine of is probably the year's total, or near it.

A New Mineral from a Gold-washing Locality in the Ural Mountains.

SOME time ago I acquired through a friend two small glass tubes, together containing about 5 grams of a bright greyish-yellow crystalline powder.

The manager of the gold workings in question noticed several years ago in his troughs minute quantities of the dust referred to, and commenced to collect it, but in spite of the greatest care he was not able to find more than about 10 grams during the subsequent years.

The separation of the dust has been made easier through the specific gravity of the microscopic crystals being =9. Various analyses made proved the dust to consist of about 98.5 per cent. tantalum and about 1.5 per cent. niobium, with 0.001 per cent. manganese. We have therefore a new mineral, namely, native tantalum.

During the last six months no more traces of the mineral have been found, notwithstanding the greatest possible care taken to find more. It seems to have been here an instance of an isolated formation, but it is not impossible that the same mineral may be found elsewhere, associated with gold and platinum, but is overlooked owing to the small quantity and the fact that it has a lower specific gravity than gold or platinum.

Perhaps this information may be of interest to those associated with gold or platinum workings, and may induce them to look out for this new mineral, when it is not improbable there may be found other native metals as well. Newcastle-upon-Tyne. P. WALTHER.

The Benham Top.

IN confirmation of Mr. F. Peake Sexton's contention in NATURE of September 2 (p. 275), that irradiation plays no appreciable part in the necessity for thin lines on the Benham top, I may add that the colours are equally well

A similar conclusion seems to be arrived at by a comparison of Greenwich and Rothesay weather. It appears (whatever the explanation) that when the year's rainfall at Rothesay has exceeded 55 inches (last year had 56), the following summer at Greenwich has never been very seen We may tabulate the cases (eleven in number, 1841-1907) as follows:

warm.

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a when the top is viewed (1) through narrow diaphragm held close to the eye; (2) through a magnifying lens; (3) in the monochromatic light of the sodium flame.

My only objection to Mr. Sexton's theory was at first the brilliancy of the colours in the light of the sodium flame, but this difficulty at once disappeared when Mr. Sexton pointed out that though blue objects cannot be seen as such in that light (because there are no blue rays present for them to reflect), it by no means follows that the nerve centre for blue cannot be stimulated by the light of a sodium flame. It will be seen, on reflection, that quite different phenomena are involved in the two cases, and, this understood, there seems to be no difficulty in accepting Mr. Peake Sexton's theory, which is substantially similar to that of Prof. Liveing, made at the time the top first appeared, though Prof. Liveing did not seem to realise that the case of the sodium flame presented no real difficulty, and he suggested that the colours seen in that light were due to the fact that it is not absolutely monochromatic-a quite unnecessary contention.

Colchester, September 8.

CHARLES E. BENHAM.

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