REVIEWS 66i 



published or revised recently enough to embody the many important results 

 and theories which have marked the strikingly rapid advances of this science 

 within recent years. English students are therefore under a double debt 

 of gratitude to ]Mr. Jones for the delightfully readable and up-to-date work 

 which he has written under the above title. It is equally valuable as an 

 introduction to astronomy for first-year students, or for the general reader 

 who wishes to be au fait with the latest researches. All the numerous 

 branches of the subject are dealt with, though none but the most elemen- 

 tary mathematics are employed, so that it is scarcely to be expected that 

 any considerable amount of detail would be included. Nothing of great 

 importance, however, has been omitted, and it is surprising how much has 

 been compressed into one volume without loss of clarity. 



The avoidance of mathematics renders the treatment of spherical and 

 dynamical questions rather difi&cult. The usual lines are followed, for the 

 most part, in these sections, and some problems (such, for example, as the 

 inequalities of the lunar motion) are explained with admirable clearness to 

 the non-mathematical reader. A paragraph is also included on latitude 

 variation which is not usually to be found in works of this class. 



The author is rather inclined to be dogmatic on some points which at 

 present may still be regarded as open questions. For example, the con- 

 ception of the moon as a " dead " world showing no evidence of change 

 is strongly opposed by several astronomers ; the distances of stellar clusters 

 as found by Shapley are also not yet universally accepted. Several mis- 

 takes occur throughout the book, but are not, in general, of very great im- 

 portance and will doubtless be rectified in a later edition. It may be of 

 use to mention here a few of the more misleading examples. On p. 285 

 " Betelgeuse " should read " Arcturus " ; in the table on p. 313 the spectral 

 type of Procyon should be F5 ; the majority of the cluster variables have 

 shorter, not longer periods than the original cepheids (see p. 343) ; S Persei 

 (for Algol, on p. 345) should be ^ Persei. 



Perhaps the most interesting portion of the book is that contained in the 

 last three chapters, in which are described all the most important recent 

 developments in sidereal astronomy. In addition to the usual material, 

 prominence is given to the measurement of angular diameters of stars, Adams' 

 spectroscopic method of parallax determination, star streaming, and other 

 statistical investigations, ionisation in stellar atmospheres, Eddington's 

 researches on the interior of stars, recent cosmogonic theories, and other 

 important questions of present-day astronomy. There appears, however, 

 to be no description of the calculation of parallaxes from group motion 

 among stars, which is an accurate and in many cases extremely important 

 method of deriving stellar distances. The apex of the sun's way is superior 

 to the intersection of the equator and galaxy as an origin for galactic longi- 

 tudes. Its use is strongly advocated by some astronomers, and might 

 have been referred to, since it abolishes the effects of precession. Mention 

 might also have been made of Lockyer's theories in connection with stellar 

 evolution and spectral type, which in essence were similar to those of Russel 

 though reached independently. 



The diagrams and illustrations are both excellent and well chosen through- 

 out. The 24 beautiful plates add greatly to the value and charm of an 

 interesting and well-written textbook. D. L. E. 



The Elements of Astronomy. By D. N. Mallik, B.A., Sc.D., F.R.S.E., 

 Professor, Presidency College, Calcutta. [Pp. 8 -|- 233, with 109 dia- 

 grams.] (Cambridge : at the University Press, 1921. Price 14s. net.) 



The publisher's notice on the wrapper of this book states that " The author's 

 object has been to give a brief and clear account of those portions of 

 Astronomy which can be dealt with, with the help of elementary mathe- 



43 



