296 



NATURE 



[September 8, 1910 



or pleasure, and desire to have some knowledge 

 of the principles underlying the design and working 

 of the particular machines they employ. The steam 

 turbine has been rather inadequately treated in com- 

 parison with the reciprocating^ steam eng:ine, but por- 

 liaps this was inevitable in a book of this nature, as 

 the latter is still ])ractically unchallenged by its 

 vounger rival in manv branches of work in which 

 motive power is required. 



This is a book which will probably stimulate many 

 of its readers to widen their knowledj^e of the 

 problems concerned with the generation of energy, 

 and to devote themselves to a systematic study of the 

 subject, and, if it fidfils this, it will have done useful 

 work. T. H. B. 



Photomicrographs of Botanical Studies. Pp. 62. 



(MiVichester : Flatters, Milborne and McKechnie, 



Ltd., n.d.j Price 2s. net. 

 This booklet contains about a hundred plates, which 

 are photographic reproductions from the microscopical 

 slides offered by the firm above-mentioned for the use 

 of botanical students. The chief impression conveyed 

 by the fifjures is the limitation imposed upon good 

 microscopical preparations when referred to one focal 

 plane as necessitated by photofjraphy. While the 

 value of fTOod slides for demonstration and examina- 

 tion by students is appreciable, one cannot attach 

 inuch importance to figures which are primarily in- 

 dices and convev in many cases onlv a portion of the 

 information that can be derived from the preparations. 



Illustrated Guide to the Museum of the Royal College 

 of Surgeo)is, England. Pp. vi+132. By Prof. 

 Arthur Keith. (London : Issued by order of the 

 Council of the College, and sold bv Taylor and 

 Francis, igio.) Price 6d. 

 Few even of those who constantly make use of the 

 College of Surgeons' Museum can be aware of the 

 vast wealth of material stored there. For it contains 

 not only the greatest anatomical collection in exist- 

 ence, representative of everything included under the 

 term " anatomy " in its widest sense ; but it also in- 

 cludes a unique pathological museum, and collections 

 illustrating anthropology, teratology, odontology, and 

 the anatomy of animals and plants, each of which, if 

 standing alone, would make a famous museum. Nor 

 does this exhaust its claims on our interest, for in 

 it is housed the famous collection made by John 

 Hunter, innumerable anatomical and pathological pre- 

 parations that have served as material for the master- 

 builders of the sciences of anatomy and pathologv, and 

 specimens illustrating the history of all that relates 

 to the preservation of dead bodies (starting from the 

 earliest known mummy), the evolution of surgical and 

 dental instruments, and the manifold curiosities of 

 medical science which at various times engaged the 

 attention of the ever-inquisitive Hunter. 



The council of the college has earned the gratitude 

 of a very wide circle of students in issuing this 

 "guide," which .admirably serves its purpose of indi- 

 cating what the museum contains and where the 

 various specimens are to be found, and Prof. Keith 

 deserves our heartiest congratulations on the manner 

 in which he has accomolished his task. For he has 

 done something more than merely direct the reader 

 in his wanderings through the vast storehouse of 

 treasures in his charge; out of the abundance of his 

 knowledge and erudition he has crammed a vast 

 amount of interesting and suggestive information into 

 this small volume. 



This is only one, and bv no means the least, of the 

 many great services which have .alreadv marked Dr. 

 Keith's conservatorship of the college museum. 



NO. 2132, VOL. 84] 



The Photographic Annual, igio-ii, Incorporating the 

 Figures, Facts, and Formulae of Photography. .A 

 Guide to their Practical Use. Edited by E. J. Wall. 

 .Sixth edition ; extended, largely re-written, and re- 

 vised. Pp. viii + 287. (London: G. Routledge and 

 Sons, Ltd. ; Dawbarn and Ward, Ltd. ; New York : 

 Tennant and W'ard ; Melbourne: Baker and Rouse 

 Proprietary, Ltd., 19 10.) Price is. net. 

 Every photographer knows the value and utility of 

 this annual issue, and that this is the sixth issue is 

 suflicient testimony to its merits. There is no doubt 

 that, in preparing such a work as this, and to keep 

 the volume within a reasonable size, great difficultv 

 must be experienced in determining what information 

 to include or omit. The editor has used his dis- 

 cretion wisely, with the result that the present issue 

 should meet with general approval among photo- 

 graphers. 



The importance and recent advances made in screen- 

 plate colour-photography is sufficient reason for the 

 first forty pages being devoted to this subject, and 

 here the reader will find a capital resume of the state 

 of affairs up to the present time. Stereoscopic work 

 is next dealt with, and in the twenty-seven pages in 

 which this subject is treated many useful hints will be 

 found. Nearly the same amount of space is confined 

 to some useful notes on development, including time, 

 tank, and thermo methods. Practically the remainder 

 of the book is taken up by the figures, facts, and 

 formulae, which always form the chief feature of this 

 book. 



Being well up-to-date and in a handy form the book 

 should continue its useful career. 



LETTERS TO THE EDITOR. 

 [2'he 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 

 mamiscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications.] 



The Ratio between Uranium and Radium in Minerals. 



In his interesting letter (Nature, August 25) Mr. A. S. 

 Russell describes the result of a determination of the 

 amount of radium in a specimen of autunite from Autun, 

 France, made by him in Prof. Marckwald's laboratory, 

 which he found to be only 27 per cent, of the equilibrium 

 amount. The ratio found by Mile. Gleditsch in Mme. 

 Curie's laboratory for the same mineral was 80 per cent., 

 while Miss Pirret and I recently, for an autunite from 

 Guarda, Portugal, found 44 per cent. Some results I 

 have obtained since the paper with Miss Pirret was pub- 

 lished appear to put a new complexion on the matter. 

 Dual measurements of the radium ratio and of the helium 

 content of several specimens of Portuguese autunite have 

 .shown that both vary considerably for different specimens 

 of the same mineral. Prof. Piutti (" Helium in Recent 

 Minerals," Le Radium, icjio, vii., 17S) found that autunite 

 was the only radio-active mineral in which helium could 

 not be detected. 



With a very delicate method, similar to that described 

 for the detection of the helium produced from uranium and 

 thorium (Phil. Mag., August, iqoS), I have only failed to 

 find helium in one specimen of autunite, while in another 

 the amount was such that Prof. Piutti would have 

 detected it easily. The latter case refers to the specimen 

 for which Miss' Pirret and I found 44 per cent, for the 

 radium ratio. The amount of helium was 3-3 cu. mm. 

 per gram of uranium. On the assumptions, which 

 certainly are not true but may not lead to an entirely false 

 result, that the uranium w-as initially free from all pro- 

 ducts, and these have been all retained by the mineral, the 

 age of the mineral would be 77,000 years and the period 

 of average life of the parent of radium 132,000 years. 

 The material was, however, not a single piece, a batch of 



