378 



NATURE 



[July 6, 191 6 



of the lines of metallic vapours, the spectra of 

 carbon and its compounds, the ultra-violet spectra 

 of the elements, the emission spectrum of water 

 vapour, the spectrum of magnesium, the absorp- 

 tion spectrum of oxygen, and the spectra of the 

 rare gases. There are also several papers refer- 

 ring to new forms of spectroscopes or details of 

 instruments. 



The general impression conveyed to the re- 

 viewer by the volume is not so much of striking 

 discoveries as of a steady output of careful work 

 which almost invariably contributed materially to 

 the general advance of spectroscopy. Neverthe- 

 less, only a small part of the work can be de- 

 scribed as having been of a routine character, 

 and the papers have a special value on account 

 of the great variety of experimental methods 

 devised by the authors with definite objects in 

 view. Thus the student or the beginner in spec- 

 troscopic research will find an abundance of useful 

 hints on manipulation which it would be difficult 

 to find in a convenient form elsewhere. 



Perhaps the most laborious piece of work 

 undertaken by the authors was that on the ultra- 

 violet spectra of the elements, which involved the 

 taking of some thousands of photographs, and 

 the determination of wave-lengths under conditions 

 much more difficult than would be the case at the 

 present time. The recognition of "harmonic 

 series " of lines, with alternating sharp and 

 diffuse members, was a notable outcome of this 

 work, and although the authors were not com- 

 pletely rewarded by the discovery of the laws of 

 spectral series, their observations greatly facili- 

 tated the subsequent investigations of series lines 

 by Rydberg. 



Spectroscopy is full of pitfalls, largely on 

 account of the difficulty of preparing perfectly pure 

 substances for experiment, but the authors have 

 had the satisfaction of themselves correcting some 

 of their misinterpretations of observations, as in 

 the case of certain silicon lines at first assigned 

 to carbon, and a triplet of the Swan spectrum 

 attributed, in the first instance, to cyanogen. It 

 might have been expected, however, that they 

 would have taken advantage of the opportunity 

 of indicating, by footnotes or otherwise, further 

 developments in connection with some of the sub- 

 jects dealt with. It might have been pointed out, 

 for example, that about 50 per cent, of the un- 

 identified lines of atmospheric gases not con- 

 densed at the temperature of liquid hydrogen are 

 accounted for by the second spectrum of neon 

 discovered by Merton. 



The publication of this volume can scarcely 

 fail to stimulate further research in many 

 directions. One point which has received 

 less attention than it deserves is the ob- 

 servation by the authors that the mixed vapours 

 of magnesium and sodium, in their experiments 

 on reversals, yielded an absorption line about 

 wave-length 5300, which did not appear with 

 either vapour separately, or when sodium was re- 

 placed by potassium. Other lines were similarly 

 found to be characteristic of a mixture of mag- 

 nesium and {X)tassium. Since mixtures of vapours 

 NO. 2436, VOL. 97] 



are involved in the sun and stars, as well as in 

 many of the laboratory applications of spectrum 

 analysis, the possibility of the development of 

 lines characteristic of mixtures would appear to 

 be of fundamental importance. There are pro- 

 bably few observations which favour this supposi- 

 tion, but a more extended investigation is cer- 

 tainly desirable. 



The volume concludes with a supplementary 

 memoir, not previously published, on the separa- 

 tion of gases by electric discharges with various 

 electrodes. It fully maintains the high standard 

 of the earlier investigations, and will be appre- 

 ciated, for example, by anyone who has attempted 

 to prepare a vacuum tube of oxygen uncontami- 

 nated with carbon impurities. 



The authors may well take pride in this hand- 

 some record of their long-continued labours in the 

 field of spectroscopy, but it may be hoped that 

 the volume is not intended to mark the termination 

 of their contributions to the subject. 



YORKSHIRE TROUT FLIES. 

 Brook and River Trouting: A Manual of Modern 

 North Country Methods, with Coloured Illus- 

 trations of Flies and Fly-dressing Materials. 

 By H, H. Edmonds and N. N. Lee. Pp. 106. 

 (Bradford : Published by the Authors.) Price 

 los. 6d. net. 

 nPHIS is an attractive little book, well produced, 

 -L admirably illustrated, and written by two 

 anglers who obviously know their subject. As 

 what may be called a "local " manual it is as good 

 as anything that has been produced for a long 

 time. It has special claim to consideration in its 

 handling of the question of flies. The authors 

 select some three dozen patterns, commonly and 

 profitably used on north-country streams, and 

 make it possible for the amateur fly-dresser to be 

 sure of getting them right by giving, besides the 

 verbal instructions, coloured plates which -show 

 both the flies and the materials of which they 

 are made. One plate also gives the colour shades 

 by which fly-tying silk may be matched. The 

 result is a really practical text-book on which, so 

 far as it goes, the amateur can safely depend. 

 No doubt it will be apparent to many readers that 

 it might go farther, and that a good many 

 favourite flies are omitted from its list. But it is 

 at any rate arguable that the list is sufficient with- 

 out them, and that an angler entirely without pre- 

 judices would do as well with it as he would with 

 any other list of similar length designed to meet 

 similar conditions. 



The authors give brief but sound instructions 

 as to methods of fishing on north-country streams, 

 fly-fishing, both wet and dry, creeper and stone-fly 

 fishing, clear-water worming, and spinning the 

 minnow. In each case they illustrate precept by 

 detailed experience, always a useful and interest-! 

 ing plan. When an angler can say "by doing 

 so-and-so I killed so many on such-and-such 

 occasions," and can describe the events which led 

 up to and characterised the successes, it is more 

 convincing than the use of bare imperatives. 



