4 02 



NAT URL 



[January 23, [919 



logical "; the wall of the perithecium in the Ery- 

 siphaceae docs not gradually rol away (p. -'73), but 

 opens by a definite rupture; and it is very hetero- 

 dox to state (p. 143) that the right way to mix 

 I In- components of Burgundy mixture is exactly 

 the same as with Bordeaux mixture. 



High praise must be given to the printers tor 

 surmounting so successfully the special difficulties 

 of printing which obtain .it Calcutta; the mis- 

 prints are so rare that the two noticed may be 

 mentioned here — at p. 163 "rust-resting" is 

 printed for "rust-resisting," and at p. 353 " saco- 

 spores " for "ascospores. " 



This work, which is particularly delightful in 

 its readable quality, will inevitably become the 

 "classical " book of reference for both the culti- 

 vator and the student of mycology in India. It 

 would be well if in the next edition the author 

 gave more information on "pure culture" 

 methods, enriched as this would be by his intimate 

 knowledge of how to overcome the difficulties thai 

 result from the special climatic conditions. 



E. S. & 



THE DOUBLE-STAR WORKER'S VADE- 

 MECUM. 

 The Binary Stars. By Prof. R. G. Aitken. 

 Pp. xiv+316. (New York: Douglas C. 

 McMurtrie, 1918.) 



HP HIS book is issued as one of the series of 

 *- semi-centennial Publications of the Univer- 

 sity of California. We are informed in the intro- 

 duction that "the object of this volume is to give 

 a general account of our present knowledge of the 

 binary stars, including such an exposition of the 

 best observing methods and of approved methods 

 of orbit computation as may make it a useful 

 guide to those undertaking the investigation of 

 these systems; and to present some conclusions 

 based upon the author's own researches during 

 the past twenty years." 



The spectroscopic binaries, and also the visual 

 binaries, are regarded as "members of a single 

 species," and the development in recent years of 

 both sections has tended to show that "the only 

 differences between the spectroscopic and visual 

 binary stars are those which depend upon the 

 degree of separation of the two components." 

 Granting this, the compilation of such a volume 

 as that now under review became inevitable; and 

 no one man is more favourably equipped for the 

 task than Prof. Aitken, who, while living in the 

 midst of workers in the spectroscopic section, is 

 himself the incarnation of the visual section. 

 Although not mentioned here, eclipsing binary 

 stars are also regarded as members of the family, 

 and the exhaustive and interesting chap, vii., 

 which the author devotes to them, certainly adds 

 value to the book. There are at present" about 

 one hundred and fifty known, and the chapter is 

 based on the researches of Russell and Shapley. 



The substance of chaps, i. and ii. is historical, 

 and the author proves that, in both visual and 

 spectroscopic work, American observatories have 

 NO. 2569, VOT.. I02] 



made double-star astronomy peculiarly their own. 

 It is indeed the fact, and explains why American 

 astronomers are so prominent throughout the book. 



Chap. iii. is devoted to observational methods 

 and means, including the micrometer, resolving 

 power, and personal equation. As one would 

 expect, there is much sound and practical advice. 

 On the working catalogue, a difficult subject, it 

 is Prof. Aitken 's deliberate judgment that, under 

 average good observing conditions, the angular 

 separation of pairs measured should In- nearly 

 double the theoretical limit. Of course, observers 

 with the largest telescopes must not be bound by 

 this, for if they do not measure the very closes! 

 pairs the time devoted to their discovery is wasted. 

 The note on the non-use of diaphragms is short 

 and sound. The reviewer found a neutral-tint 

 glass at the eye-end a sufficient and more con- 

 venient help. 



In chaps, iv. and vi. the author discusses fully 

 the various methods in use for computing orbits 

 of visual and of spectroscopic binaries respec- 

 tively. He carefully points out the advantages 

 of each method, giving many useful hints, and 

 illustrations by concrete examples. These two 

 chapters have been well considered and developed ; 

 they practically exhaust the subject. 



Between these two chapters is another in 

 which will be found a welcome description 

 of the spectroscope and of the manner in which 

 accurate measures of displacement in the spectral 

 lines can be made, the photographic portion beint; 

 illustrated by a minute account of the "Mills 

 spectrograph." In chap. viii. is a table of eighty- 

 seven visual binaries "divided into two groups, 

 the first containing orbits which are at least fairly 

 good approximations, the second the less accurate 

 orbits." But as we are told that "several orbits 

 included in either one of the two groups might 

 find a place in the other," the division seems 

 superfluous. These orbits have been selected in 

 general because they are the most recently com- 

 puted. There is also a table of 137 spectro- 

 scopic orbits, but only 119 are used in the discus- 

 sions. From a number of interesting results we 

 extract the following relations between the periods 

 and eccentricities : — 



46 spec, bin., mean period 275 days, ecc. 



19 „ „ „ ,. 7'8o „' „ 



„ „ „ 2300 



25 „ ,- 



29 ,. 



30 vis. bin. 



i'5 years 



74'4 

 1700 



0-047 

 0-147 

 0324 

 0350 

 0423 

 0514 

 0539 



A relationship so definite must have a physical 

 significance. Later, on p. 221, it is shown that 

 in the Cepheid variables this relation does not 

 hold. 



Treating of relative masses of visual binaries. 

 Prof. Aitken remarks: "The most reliable 

 values are those deduced by the late Lewis Boss," 

 and the table on p. 216 is constructed on this 

 idea, the work of several other computers being 

 omitted. This is a pity, and the author himself is 

 not convinced, for later he tells us that Boss 



