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THURSDAY, SEPTEMBER 16, 1909. in lucidity of exposition and accuracy of statement.

For students it will be of the greatest value, as the PRINCIPLES OF IGNEOUS PETROLOGY.

original memoirs are loaded with detail, and much too

voluminous for their use, and no satisfactory account The Natural History of Igneous Rocks. By A. of them has hitherto appeared in English. We must

Harker, F.R.S. Pp. xvi + 384. (London : Methuen, confess, however, to a certain feeling of disappoint1909.) Price 125. 6d. net.

ment in reading them, a sense of incompleteness. FOR OR some time the need of a text-book of general | The a priori principles are laid down in a very satis

petrology in English has been acutely felt, owing factory fashion, but the applicability of these printo the rapid progress which the science has made in ciples to the actual concrete facts of rock structure theoretical subjects and the inaccessibility of many and history, which we had a right to expect from a of the original memoirs to students and teachers. geologist of Mr. Harker's wide experience, is disMost text-books treat the subject from a purely missed with scant treatment. The difficulty of interdescriptive point of view, and the speculative develop- preting the history of crystallisation in the commonest ments are kept in the background. In fact the litera- rocks in terms of the theoretical principles laid down ture of descriptive petrology is now so large that an is sure to face the student at an early stage in his attempt to extract the general conclusions to be studies. We miss in particular any reference to the deduced from the observations becomes of greater work of Schreinemaker, who has proved by analytical importance than merely to add to the number of investigations that in a solution of three minerals in ascertained facts. In a book of about four hundred one another, of which two can form mixed crystals, pages Mr. Harker endeavours to meet this demand, while the third is independent, there are many possible and has covered so wide a range and compressed so schemes of crystallisation; one mineral may separate much information into this brief space that he has out completely at an early stage, and the crystallisaachieved a very large measure of success.

tion of any substance may be interrupted or repeated, The work is confined to the investigation of the If there are more components, or if we allow for the principles of igneous petrology, and the metamorphic influence of dissolved gases in the magma, the problem and sedimentary rocks are excluded from its scope. becomes much more complicated; but it is a relief to The title fairly expresses the aims of the book; it is find that as the theory is better understood the disan attempt to treat of igneous rocks in the manner crepancies between it and the observed facts seem to of natural history, taking account not only of their diminish. minute anatomy and structure, but also of their dis- The subject of “hybridism,” or mixed rocks, is tribution, their range in time, and their genetic asso- discussed in a brief chapter, which sums up in admirciations. Of late years there has been a plethora of able fashion the results of the author's work in this unnatural systems of petrology, based on purely difficult field. He takes a middle position between arbitrary lines. On the best known of these (the the schools of petrology which deny that igneous “ quantitative classification”) the author passes severe rocks dissolve sediments or older rocks with which judgment, and returns to the broader treatment they come into contact, and those which hold that followed by Rosenbusch, Brögger, Judd, and Teall. such processes go on on a large scale, and that many That combination of geological reasoning with petro- rocks generally regarded as of normal types are thus logical analysis which has always characterised the produced. Mr. Harker's field work enables him to English school of petrologists finds able expression in speak on this subject with great authority, and his the pages of this treatise.

conclusions are so moderate and so firmly based on The geographical distribution of recent volcanic sound evidence that he carries us with him in all rocks is considered in the introductory chapters, and that he says. There is also a chapter on magmatic the remarkable association of Atlantic " and differentiation, a subject on which it does not seem “ Pacific ” rock types with certain classes of tectonic possible to say anything that is new, and a very developments is made the foundation of an appeal for interesting account of the mutual relations of assoa natural classification. Undoubtedly the facts are ciated igneous rocks which, in our opinion, is the best mnost impressive, though we are entirely in the dark in the volume. The curves drawn on a very simple regarding their causes; and they afford the clearest graphic system show the variation in the components indication that in time we shall be in possession of of allied rock types, and are convincing that some natural systems of petrography. We learn incidentally general principles must underlie the facts, though as that the first sketch of this grouping was presented yet we have been unable to grasp them. The final by Mr. Harker, though it has become more generally chapter on classification is unexpectedly brief, and known through the treatment of Dr. Prior and Prof. contains an admission that existing systems are Becke. The Tertiary volcanic rocks of the Inner merely temporary stop-gaps, and a satisfactory classiHebrides are placed among the Pacific types, a con- fication must traverse the lines of all current groupclusion by no means easy to accept, and one which ings, and will require an entirely new nomenclature. may need to be revised at some future date.

To us this appears unduly pessimistic, and we believe The application of physical chemistry to the crystal- rather that in petrology as in other sciences the lisation of magmas

taken up in considerable detail. future will be the child of the past, and that real This part of the book is practically a summary of progress will not involve the demolition of the older Prof. Vogt's papers, and leaves nothing to be desired systems, but will include them while giving them a

as

THE

ar | Most of these are, however, but trifling errors,

Bv

THIS

sounder basis to rest upon. The book contains two of the forefoot fully extended when the animal is on beautiful photographic plates of active volcanoes, and land, in place of being folded beneath the palm, as a large number of useful illustrations; in print, paper, it must be in order that the creature should get a and binding it will meet the approval of every book- foothold. lover.

J. S. F. 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 A POPULAR MAMMAL BOOK.

no mention is made of the fact that the species Wild Beasts of the World. By Frank Finn.

occurs in the Bahr el Ghazal; while the occurrence Pp. viji+ 188; illustrated. (London and Edin- of the water-chevrotain in East Central Africa is burgh: T. C. and E. C. Jack, 1908–9.). Price 175. ignored. The old error to female takin-horns net.

differing in form from those of the male is also reCHE favourable opinion we formed of Mr. Finn's peated.

work when the first part was noticed last year in NATURE we are pleased to be able to endorse now which detract but little from a work worthy in the that the complete volume is before us. The book is main of high praise.

R. L. .confessedly a thoroughly popular one, and, therefore, ought to be judged solely from that standard; and

APPLIED MECHANICS. from that point of view it may be pronounced a deeided success.

The author's style of writing is bright (1) Applied Mechanics for Engineers. A Text-book for and attractive; and in the main his descriptions

Engineering Students. By E. L. Hancock. Pp. xi+ appear correct and up to date. Mr. Finn has not

385. (New York: The Macmillan Co., 1909; overloaded his text with names of naturalists and

London: Macmillan and Co., Ltd.) Price 8s, 6d. observers about whom the public knows little or

net. 'nothing; and he has, in our opinion for the most (2) Machines-Outils, Outillage, Verificateurs. " part rightly, altogether ignored subspecies. As

P. Gorgeu. Pp. 232.

(Paris : Gauthier-Villars, :regards nomenclature, the author will have nothing 1909.) Price 7 francs, 50 centimes. to do with modern innovations and changes, and we (1) HIS book is intended to be a text-book for accordingly find the baboons (and not the flying

engineering students during the first year lemur) appearing under their old title of Cyno- of their course, and the examples selected to illustrate cephalus, and the fox as Canis vulpes. The fact that the principles discussed are, therefore, mainly such as such names still dominate in popular literature sug- are likely to be met with in practical engineering gests that they. should not, as is now too much the work. To facilitate the working out of the numerical fashion, be ignored in our museums, which are problems, of which there are nearly 300 scattered primarily popular institutions.

through the book, the author has printed in the form Mr. Finn appears to take as his texts the hundred of five appendices a series of tables including hypermammals represented in the coloured plates, as the bolic functions, logarithms of numbers, trigonometridescriptions of all these are printed in larger type cal functions, squares, cubes, square roots, conversion 'than is conceded to many of the others noticed. Per- tables, &c.; it is very problematic as to how often such sonally we are not enamoured of this plan, as it tables incorporated in a text-book are of use to the suggests that the species to which large type is student—it is much more convenient for him to have accorded are of more importance than the rest; but a small thin book of mathematical tables, and there this' point is not one affecting the character of the

are several such books now available, which he can work as a whole.

carry about with him in his pocket, and refer to The coloured plates form, of course, the charac

whenever calculations have to be made. teristic of the volume which will appeal most

Two very complete chapters are those devoted to strongly to the general public; and for these illus- centre of gravity and moment of inertia ; the applicatrations—the only ones in the book-we have in the tion of Simpson's rule to the finding of the area and main nothing but commendation, although some

centre of gravity of rail and similar sections is fully appear rather too brilliantly coloured. A few, more- discussed, and the whole subject of the determination over, do not indicate important details--notably the one

of moments of inertia of various standard sections is of the hamster, in which the dorsal gland-patch is treated very fully, both by analytical and graphical not shown. The one serious error in the illustrations methods : this is a matter of considerable interest to occurs in part xii., where the plate lettered Marco engineers engaged in structural design work. Polo's wild sheep really represents the true argali Another chapter which will be found of use by the (Ovis ammon); and there is no excuse for this, as engineer in practice as well as by the young student the figures, if we mistake not, have been drawn from is that dealing with the dynamics of machinery : after the mounted specimens in the British Museum. Nor dealing with such usual problems as those of the is this all,' for, whereas the figure in the foreground flywheel and connecting-rod in a reciprocating engine, depicts, as we have said, the true Altai argali, the a number of sections is devoted to the gyroscope, and one in the middle distance is taken from its Tian to its application to the mono-rail and similar Shan representative. In the concluding part we

devices. notice that the plate of the platypus shows the web The last chapter in the book treats of impact in a

, .)

are

more satisfactory manner than is usually the case in

A BELGIAN BOTANIST. text-books on mechanics. The book is certain to Notice sur Léo Errera. By L. Frederica and J. prove a useful one to all those who are engaged in Massart.

Pp. 153.

(Bruxelles : H. Lamertin ; teaching the subject of mechanics to engineering London : Williams and Norgate, 1908.) students, and the number of well-selected examples Recueil d'Euvres de Léo Errera. Vols. i. and ii. makes it a particularly satisfactory book for the Botanique générale. Pp. iv +318 and v+341. Vol. student himself. Many young engineers are far away iii. Mélanges Vers et Prose. Pp. xiv +222. from help in matters of this nature, and have to depend (Bruxelles : H. Lamertin; London : Williams and upon their own resources--it is essential in such a Norgate, 1908-9.) case that they should have a large number of practical Problems to work through in order to familiarise IT would be difficult to overestimate the influence

of the two great German professors, Anton De themselves with the principles underlying each branch Bary and Julius Sachs, on the progress of botany. of the subject.

At a time when many fundamental ideas were only (2) This book has been written specially for artillery beginning to take shape, these advanced workers and officers detailed for duty in ordnance factories; it is

leaders of thought attracted a succession of brilliant copiously illustrated, and special attention has been

students from given to the relative advantages and disadvantages of absorbed in Strassburg and Würzburg the doctrines

many European countries, who different types of machine tools, and to different

and inspirations of their masters, and eventually methods of transmitting motion to the tools.

spread abroad the new theories and conceptions that The first section is devoted to such details as the transmission of motion from one shaft to another by science. Amongst this band of eager students was

now regarded as the foundations of botanical belting and gearing, quick return motions, cams,

the Belgian, Léo Errera, who entered first De Bary's sliding pairs, turning pairs, and screw pairs, and in laboratory in 1897, and subsequently sought further each case brief notes are given as to the important experience under the tutelage of Sachs. Two importpoints to which attention should be paid in order to

ant results can be traced to these courses of foreign secure good results and to maintain all working parts study. In the first place, intercourse with such gifted in good order.

teachers and with brilliant colleagues helped to stimuThe second section deals with all the more impor- late the energies of an already keen enthusiast, and tant machine tools which are to be found in a modern

to pave the way for future friendships and associa. workshop; in each case a regular order of treatment

tions. In the second place, his interests were diverted is followed-first the parts exterior to the machine

from systematic to chemico-physiological botany, itself and transmitting motion to it are discussed, and

which became one of the chief lines of research at then in order the links in the machine receiving this

the University of Brussels. motion, the links of the machine transmitting move- The first of his primary contributions to science merft to the work, the links of the machine trans

was the paper on glycogen in the. Mucorineæ; this mitting movement to the cutting tool, and lastly any

was the outcome of research in De Bary and Hoppeother specialised link, and the frame. This is a

Seyler's laboratories, and required a profound knowmethod of treatment suitable not only for the non

ledge of the two sciences of botany and chemistry: technical student, but also for students who are just it was followed by other papers on the same and beginning the study of machines and machine tools,

other physiological subjects published by himself or and the illustrations, which form a special feature of his students. Prof. Errera was also well yersed in the book, are so arranged that the reader has no difti- mathematics and physics, evidence of which is furculty in finding at once in any of the figures the nished by the course of molecular physiology prelink of the machine which is described in any pared for his advanced students. The researches conparticular paragraph of the written description of the nected with glycogen and the localisation of alkaloids, machine.

the papers on the application of physical chemistry The third section deals with the cutting tools used to the elementary phenomena of cells, the relations in the various types of machine tools, methods of of flowers and insects, and the defensive structures tempering, angles for the cutting edge for different of plants, may be regarded as his chief contributions classes of work, methods of lubrication, and speed of to botany. cutting are all discussed in detail, and a few para- As a professor, Errera took the keenest interest graphs are devoted to the employment of the new in his students, and spared no pains to stimulate high-speed steels.

their energies towards the acquirement of knowledge In view of the fact that interchangeability of parts and the prosecution of research. At the time when is now so important in all cases where large numbers practical courses were not yet customary he initiated of similar machines are constructed, the fourth section a course which was first held in two small rooms in is entirely given up to an account of the construction the gardens, and later in a more spacious laboratory and use of various types of gauges, with a series of provided at his own expense in a neighbouring builduseful notes on the precautions which must be adopted ing: The biography compiled by two of his former to ensure that their employment shall secure the students bears testimony to the enthusiasm he indesired result. The book should be consulted by all spired, and provides a realistic picture of his varied those who are engaged in the design of machine talents. . He was an accomplished linguist, an excele. tools.

T. H. B. lent lecturer, and an entertaining companion.

to

The papers on general botany collected in the two illustrate the calcification of the temporary teeth and volumes noted above are of a popular nature, as his their change to the successional set; amongst other more technical contributions have been published in points clearly shown, the extent of calcification in each the Recueil de l'Institut botanique de l'Université tooth, at each age, a point sometimes of medicolegal

importance, is well seen. Some points in the relation de Bruxelles. The first is a letter describing the of the growth of the jaws to the development of the vegetation in the neighbourhood of Nice, written teeth can be advantageously studied in these skiawhen he was sixteen years old. The article on the grams, as well as the relation of the developing teeth structure and methods of fertilisation of flowers to the antrum. Inasmuch, however, as the walls of appeared four years later; it was inspired by Charles

the antrum cannot always be very clearly traced in Darwin's work, and the introductory quotation from jaws, the anatomy of the antrum is also illustrated

the midst of shadows cast by other parts of the upper the “ Origin of Species," taken in conjunction with by drawings made subsequently from the same his essay on Darwinism, is worth reproducing :- specimens, the technique adopted being to harden the “Whoever is led to believe that species are mutable tissues in formol, and then to chip away as much of will do good service by conscientiously expressing his the bone as could be removed without destroying all convictions." The article is, to a large extent, an

support. The lining membrane so treated becomes account of contemporary investigation, but includes sufficiently firm to stand alone and retain its

shape. original notes on the oxlip and the genus Pentstemon. figures include also the accessory sinuses. The

and the dissections made were carefully drawn. These The essay entitled “Une Leçon élémentaire sur le authors may be congratulated upon having produced Darwinisme” was revised in 1903, after the publica- | an atlas which is of the greatest service in adding to tion of de Vries's book. Errera fully accepts the the accuracy of our knowledge of the development of mutation theory, regarding it as an amplification, and the teeth and of their relations to the parts about not a contradiction, of the selection theory. The

them. references in this paper

Dr. Scott's work on

Mineralogie und Geologie für schweizerische Mittel

schulen. By Dr. Hans Frey. Dritte Auflage. Pp. Cheirostrobus and the joint communication by Drs.

iv.+234. (Vienna: F. Tempsky; Leipzig : G. FreyScott and Oliver on Lagenostoma will serve to indi

tag, 1909.) Price 2.75 marks. cate how the author incorporated the very latest re- This work, which has evidently been successful, is sults into his teaching.

of the type commonly used in German-speaking The most interesting part of the third volume, con- schools, and makes no special appeal to the beginner's taining miscellaneous verse and prose, will be found in interest in field-observation, or to the splendid objectthe collection of extracts and aphorisms. Here is an Switzerland. A number of Swiss illustrations are,

lessons ranged around him in his native land of epigram that will be appreciated by philosophers however, inserted, and the passages on mountaingenerally :-“La vérité est sur une courbe dont notre building and the Alpine lakes embody considerations ésprit suit eternellement l'asymptote.” The authors raised in recent times. To a British mind the of the biography are to be congratulated on present- mineralogical section will seem to contain far too ing such an interesting account of the brilliant much in a small compass, if the course is to be gone alumnus of Brussels University. The papers are

through systematically before the pupil enters on his

collegiate years. It occupies half the book, and is worthy of consultation, not alone for the facts con

followed by a petrographic chapter, which similarly tained, but also for style and arrangement.

bears traces of having been brought somewhat

hesitatingly towards modern modes of statement and OUR BOOK SHELF,

classification. An Atlas of Skia grams, illustrating the Development The section on historical geology, perhaps in accord

of the Teeth, with Explanatory Text. By Dr. J. ance with a settled syllabus, is limited to thirty-four Symington, F.R.S., and Dr. J. C. Rankin. pages, and the illustrations of fossils are given withPp. 47; pl. xii. (London : Longmans, Green and out any explanation as to the nature of the organisms. Co., 1908.) Price 1os. 6d. net.

In these circumstances, the generic and specific names THE difficulty of cutting sections comprising both soft

are worse than useless; they need, moreover, some and highly calcified parts without causing displace- revision and press correction. A great opportunity ments, and the further trouble of piecing together the

still remains for making the mineralogy and geology disposition of parts in a large number of serial sec

of Switzerland serve an introduction to these tions so as to reconstruct a model in the solid, gives sciences, and for letting the land itself speak to the to skiagrams an especial value, as being a representa- pupil, before he becomes entangled in the strings of tion of the relations of the developing teeth to one

facts which are supposed to be inseparable from a another and to the jaws which is beyond suspicion scientific education.

G. A. J. C. of disturbance. Certain difficulties arising from the Gilbert White and Selborne. By Henry C. Shelley. teeth being disposed in an arch were very successfully Illustrated from photographs by the author. Pp. met by the authors, who resorted to tipping the back xvi+226. (London: T. Werner Laurie, 1909.) of the skull upwards to a uniform extent in all cases, Price 6s. net. namely, raising the back about 30 degrees, and by This little book is not badly done so far as it goes, but this method the shadows of the front teeth were there is nothing in it that has not often been said separately projected and the overlapping of the before; the photographs are good, but of quite familiar shadows to a great extent avoided. The skulls used objects. The one innovation consists in eking out a were divided into halves, and the right and left sides volume offered at six shillings by “ Cameos from the both presented in nearly every case where the skulls Natural History of Selborne," which occupy fifty of used were more than seven years of age; but in the these meagre pages : a serious literary blunder, to younger ones, no difference being found between the use a mild word. The six shillings might be much two sides, only one is presented.

better spent in the purchase of an edition of the famous The ages of the subjects used range from birth to book, which is much talked of but probably little adult life, and twenty-three skiagrams are given which read.

as

LETTERS TO THE EDITOR.

so called) to the present season, following on a Rothesay (The Editor does not hold himself responsible for opinions year, which would fall to be added to the above list.

expressed by his correspondents. Neither can he undertake Once more; the summer season of 1879 is well reto return, or to correspond with the writers of, rejected

membered as a singularly cold one. There were only manuscripts intended for this or any other part of NATURE.

thirty days with 700 or more, and one with 80° or more No notice is taken of anonymous communications.] (the averages being 77 and 15 respectively); and now, at The Summer Season of 1909.

thirty years' interval, we have another very cold summer.

Suppose we compare each summer with the thirtieth In endeavouring to estimate the character of a coming

after, in respect of those very hot days (80° or more). season, the following method is, I think, often serviceable.

We can carry the comparison obviously up to 1878 (that Let us take, as a concrete case, the annual numbers of

year compared with 1908). very hot days at Greenwich (80° or more) from 1841 to

It would appcar that, in the case of very cold and very 1908. Add these in the thirty years ending 1870, 1871,

warm summers, there is some tendency for the thirtieth 1872, &c. Then compare each sum with the next by the

after to be of like sign in relation to the average. dot method; where each dot represents one value by the

Thus the six coldest, in ascending order (o to 6 hot days), horizontal scale, and the next by the vertical. A line may

are 1860, 1862, 1841, 1853, 1855, 1845; in each case but one be drawn connecting points of intersection of lines (hori- the thirtieth season after was cold, and that one was average. zontal and vertical) from equal numbers in the two scales, and two others roughly parallel with it (as shown).

The six hottest, in descending order (40 to 27, hot days),

are 1868, 1857, 1859, 1846, 1876, 1870; in each case but Now the last value, previous to this summer-the sum, That is, of the thirty years ending 1908-is 417. Find this

one (again average) the thirtieth season after was hot. in the horizontal scale, and consider where the next dot is

The season of 1909 seems likely to conform to this.

ALEX. B. MacDOWALL. likely to go. It would hardly be higher than (say) the level of 433. Now we know the numbers of those days

P.S. (September 13).—There have been, so far, nine of in twenty-nine out of the thirty summers ending 1909; their

those very hot days (three in May, six in August), which

is probably the year's total, or near it. 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

A New Mineral from a Gold-washing Locality in the

Ural Mountains. the average). The season has, so far, proved a very cool one (August 4). This method is obviously capable of wide glass tubes, together containing about 5 grams of a bright

Some time ago I acquired through a friend two small application.

greyish-yellow crystalline powder.

The manager of the gold workings in question noticed

several years ago in his troughs minute quantities of the 410°20'30'40'so '60'0'80 90 100

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 490

the specific gravity of the microscopic crystals being =9.

Various analyses made proved the dust to consist of about 480

98.5 per cent. tantalum and about 1.5 per cent. niobium,

with 0.001 per cent. manganese. We have therefore a 470

new mineral, namely, native tantalum.

During the last six months no more traces of the mineral 460

have been found, notwithstanding the greatest possible

care taken to find more. It seems to have been here an 450

instance of an isolated formation, but it is not impossible

that the same mineral may be found elsewhere, associated 440

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. 430

Perhaps this information may be of interest to those

associated with gold or platinum workings, and may induce 426

them to look out for this new mineral, when it is not im.

probable there may be found other native metals as well. 40K

Newcastle-upon-Tyne.

P. WALTHER. A similar conclusion seems to be arrived at by a com

The Benham Top. parison of Greenwich and Rothesay weather. It appears

IN confirmation of Mr. F. Peake Sexton's contention (whatever the explanation) that when the year's rainfall in NATURE of September 2 (p. 275), that irradiation plays at Rothesay has exceeded 55 inches (last year had 56), the no appreciable part in the necessity for thin lines on the following summer at Greenwich has never been very Benham top, I may add that the colours are equally well warm. We may tabulate the cases (eleven in number,

when the top is viewed (1) through a 1841-1907) as follows:

diaphragm held close to the eye; (2) through a magnifying Rothesay Greenwich days

lens ; (3) in the monochromatic light of the sodium flame. with 80° or more

Relation to in.

My only objection to Mr. Sexton's theory was at first

av. (15) following summer

the brilliancy of the colours in the light of the sodium (1) 1872

70'2

16

+ I (2) 1877

fame, but this difficulty at once disappeared when Mr. 686

4

Sexton pointed out that though blue objects cannot be (3) 1841

65'9
17

seen as such in that light (because there are no blue rays (4) 1903

61.6
16

present for them to reflect), it by no means follows that (5) 1882

59-6
7

the nerve centre for blue cannot be stimulated by the light (6) 1862

59-5
13

of a sodium fame. It will be seen, on reflection, that quite (7) 1866

587
9

6

different phenomena are involved in the two cases, and, (8) 1907

58.5
8

7 this understood, there seems to be no difficulty in accepting (9) 1868

57'2
14

Mr. Peake Sexton's theory, which is substantially similar (10) 1861 56:3

- 14 to that of Prof. Liveing, made at the time the top first (11) 1906 56-3

- 13

appeared, though Prof. Liveing did not seem to realise that the case of the sodium flanie presented no real

difficulty, and he suggested that the colours seen in that That is, eight cool summers, three slightly warm, and the light were due to the fact that it is not absolutely monohottest with seventeen of those days. It seemed not un- chromatic-a quite unnecessary contention. reasonable to apply this rule-of-thumb (if it is to be Colchester, September 8.

CHARLES E. BENHAM.

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