220 



NA TURE 



[July 9, 1908 



an elementary manual to highly technical methods. 

 The last three chapters, on reagents and processes, 

 microchemistry of plant products, and detection of 

 adulterations in foods and drugs, would, if published 

 separately, provide a most useful and attractive sum- 

 mary for advanced students. 



Elements of Angling. A Book for Beginners. By 



H. T. Sheringham. Pp. xvi + z^g. (London: 



Horace Cox, 1908.) 

 \Ve always open Mr. Sheringham's contributions to 

 angling literature with the expectation of being be- 

 guiled by very pleasant reading, and, incidentally, of 

 acquiring much useful information. In the case of 

 his " Elements of Angling " we were in no wise dis- 

 appointed. The book is primarily addressed to and 

 intended for the young angler, that is, the angler 

 young in his art, for our author will not acknow- 

 ledge that any man is too old to begin ; it is wide in 

 its scope, but docs not enter into so much detail as to 

 be likely either to confuse or weary a prospective 

 fisherman. If such a term may be excused, we would 

 describe it as an elementary text-book of fresh-water 

 fishing, and, like many other text-books, we think it 

 is well worthy of study even by those well versed in 

 the subject of which it treats. 



The information and advice given are throughout of 

 an eminently practical nature, and Mr. Sheringham is 

 not above citing his own misfortunes as an example 

 and warning to those whom he would instruct. Fish- 

 ing for coarse fish, whether on the bottom or at the 

 surface, is clearly and concisely dealt with, and much 

 practical information as to gear and baits is given. 

 The trout is discussed at somewhat greater length, 

 and the differences in the tackle required for wet- 

 and dry-fly fishing, together with the reasons for such 

 differences, are clearly explained; the gravling has a 

 chapter to itself, and, as in the case of the trout, a 

 short but well-selected list of the flies of most general 

 utility is given. 



Exigencies of space prevent the salmon and salmon- 

 fishing from being dealt with at great length, but 

 this, we think, is right in the case of a fish the capture 

 of which depends so much upon a thorough knowledge 

 of liie particular water to be fished. Care is, however, 

 taken to direct attention to the differences between 

 salmon and trout, whether as parr or adults, and to 

 the difficulty which sometimes attends the recognition 

 of a well-mended kelt and its distinction from a clean 

 fish. While on the subject of specific distinctions, we 

 notice that Mr. Sheringham regards the " bull-trout " 

 as a distinct species (Sabno criox), and states that it is 

 found in the Tweed and in some rivers of the south 

 and west ; surely there is some confusion here that 

 might well be cleared up in future editions. Last, but 

 not least, there is an excellent index. L. W. B. 



Elements of the Theory and Practice of Cookerv. By 

 Mary E. Williams and Katharine R. Fisher. Pp. 

 xix+347. (\ew York: The Macmillan Co.; 

 London : Macmillan and Co., Ltd., 1907.) Price 

 4^. 6d. net. 



Domestic science and art, so far as they relate to 

 cookery, are here combined to produce an educational 

 and pra_j-tical course of work. The book is not merelv 

 a collection of recipes, but a guide to the experimental 

 study of principles and their application in the selec- 

 tion and preparation of food. The instructions for ex- 

 periments and other work are explicit, and much srood 

 advice is given as to the conditions of healthy living 

 and intelligent housecraft. L^nfortunately, as manv 

 of the terms used in describing the utensils and in- 

 gredients required are unfamiliar in British homes 

 and schools, the book is at a disadvantage on this side 

 of the Atlantic, though its merits are many. 



NO. 2019, VOL. 78] 



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 0/ Nature. 

 No notice is taken of anonymous communications.] 



Spectrum uf the Radium Emanation. 



.'\ FEW months ago, through the generosity of the 

 Academy of Sciences of Vienna, one of us was loaned a 

 radium preparation containing about 250 mg. of radium. 

 Observations were at once begun to purify the emanation 

 produced by it, and to determine its volume. An account 

 of these investigations was read before the -Academy of 

 Sciences of Vienna on July 2. It was found that the 

 ma.\imum volume of the emanation per gram of radium 

 was in good accord with that to be expected from calcula- 

 tion (about Ob cubic mm.), and the initial volume was 

 about one-tenth of that determined by Ramsay and 

 Cameron (Journ. Chem. Soc, p. 1266, 1907). In the course 

 of this work we have had occasion to test the purity of 

 the emanation by the spectroscope, passing an electric 

 discharge in the capillary in which the volume was 

 measured. We have on four different occasions during 

 the last two months determined the spectrum of the radium 

 emanation by visual observations, using a direct-reading 

 Hilger spectroscope, leaving a more accurate determina- 

 tion of its spectrum until the measurements of the volume 

 had been completed. We have now photographed the 

 emanation spectrum, using a prism of 2 inches base. Pure 

 emanation, corresponding to the equilibrium amount from 

 130 mg. of radium, was condensed by liquid air in an 

 exhausted spectrum tube of about 50 cubic millimetres 

 capacity, provided with thin platinum electrodes. Two 

 photographs were immediately taken, one giving about 

 thirty of the more intense lines, and the other, with much 

 longer exposure, showing more than one hundred lines. 

 For a comparison spectrum a helium tube was used. The 

 colour of the discharge in the tube was bluish. Visual 

 observations of the spectrum were made during the ex- 

 posure of the photographs. 



When the emanation was condensed in a side tube by 

 means of liquid air, the great majority of the lines 

 vanished at the moment of condensation, which was readily 

 noted by the phosphorescence of the glass. The colour of 

 the discharge then completely changed, and became of a pale 

 rose colour. At the instant of volatilisation, the emanation 

 lines flashed out again. The hydrogen lines were visible 

 in the spectrum, and these became much more brilliant 

 when the emanation was condensed. In the electrodeless 

 discharge of previous experiments, the hydrogen lines were 

 never observed. Their occurrence in the present e.xperi- 

 ment was probably due to the platinum electrodes. By 

 observations of the intensity of the phosphorescence when 

 the emanation was condensed, it was noted that the amount 

 of pure emanation in the tube gradually diminished with 

 increase of time of discharge. The spectrum of the 

 emanation, however, persisted until practically all the 

 emanation had been driven into the walls of the tube. 

 The phosphorescence on the walls of the tube showed that 

 the occluded emanation was fairly uniformly distributed. 

 This effect has been observed by us on several occasions. 



The first determination of the spectrum of the emanation 

 was made in 1904 by Ramsay and Collie, who determined 

 the wave-lengths of about eleven lines by visual observa- 

 tions. As shown by them, the spectrum of the emanation 

 is a bright line spectrum with sharply defined lines. We 

 observed also visually a weak band spectrum in the vellow, 

 which slightly decreased in intensity when the emanation 

 was condensed. This, however, may not be connected 

 with the emanation itself. The wave-lengths of the lines 

 of the photographic plate were accurately measured, using 

 a Kayser's measuring machine. The accuracy obtained is 

 indicated by the agreement of the wave-lengths of some of 

 the hydrogen lines with their known values. In most 

 cases, for, well marked lines, the error is not more than 

 half an .Angstrom unit. The following table "fives the 

 wave-lengths of the more prominent lines. The wave- 

 lengfths of the lines initially determined by Ramsay and 

 Collie (marked R. and C.) are added for comparison. 



