322 



NATURE 



[December 26, igiS 



spore," and "teliospore," it does appear unneces'- 

 sary to replace the convenient word "oonidium 

 by "iconidibspore. " Also, " epiphytotisms, " in 



the place of "epidemics," is rather dreadful, And 

 .1 firm protest must be made against the attempt 

 to label the "wart-disease of the potato V "chytri- 

 diose, " or we shall be required ultimately to tell 

 the farmer to call "potato-blight" " phyto- 

 phthorose " ! 



Not the least valuable part of this book, which 

 is indispensable to all mycologists, is the excellent 

 bibliography (dealing chiefly with American and 

 German authors) which is given in all the sections. 



E. S. S. 



DYNAMICAL IND POPULAR ASTRONOMY. 



(1) An Introductory Treatise on Dynamical Astro- 

 tunny. By Prof. H. C. Hummer. Pp. xx + 344. 

 (Cambridge : At the University Press, 1918.) 

 Price 1 8s. net. 



(2) The Destinies of the Stars. By Prof. Svante 

 Arrhenius. Authorised translation from the 

 Swedish by J. E. Fries. Illustrated. Pp. xviii-t- 

 256. (New York and London : G. P. Putnam's 

 Sons, The Knickerbocker Press, 1918.) Price 

 7s. bd. net, 



(1) T^HERE has long been a need for a general 

 -I- book on celestial mechanics on a 

 smaller scale and at a more accessible price than 

 the standard work of Tisserand, and Prof. 

 J Mummer's recent publication is a very successful 

 effort to satisfy that need. It is so concisely 

 written that a most remarkable amount of material 

 is made available within a limited space, with only 

 occasional loss of clearness. Halphen's theorem, 

 that if the acceleration of a particle is a function 

 of its position alone, and all the trajectories are 

 plane curves, then the acceleration is always 

 directed towards a fixed point, forms the com- 

 mencement of the problem of two bodies. This 

 constitutes a most welcome innovation, as Kepler's 

 second law now becomes a consequence of the 

 first, and its truth a confirmation of it. The 

 methods of determining from observation the orbits 

 of planets, comets, and visual and spectroscopic 

 binaries are treated in detail, and then the author 

 passes on to the treatment of perturbations, which 

 is dealt with much as usual; but it is pleasant to 

 sec that chap, xvi., on secular perturbations, in- 

 cludes a table of numerical results. Very useful 

 features are the account of recent work on 

 methods of numerical interpolation and integra- 

 tion, and the description of Cowell and Crom- 

 melin's method of computing special perturbations. 

 The lunar theory and the theories of precession, 

 nutation, and lunar libration are also discussed in 

 some detail. Misprints are few and the index is 

 good. The present writer would like to suggest, 

 however, that in a future edition tables of the best 

 available values of the elements of the solar 

 system, in astronomical and metrical units, should 

 be included; for these are the fundamental data 

 of dynamical astronomy, and are not usually pre- 

 ted in any convenient form. 

 NO. 2565, VOL. I02] 



(2) Prof. Arrhenius's work is a popular account 

 of three very different astronomical subjects. Tin 

 first chapter deals with the influence of the 

 heavenly bodies on primitive human thought, 

 describing how the moon's phases came to be 

 used as a basis of chronology, on account of their 

 easily recognisable variability, and how with the 

 advance of culture the importance attributed to 

 the year and the sun increased. The earl)' know- 

 ledge of the major planets is also discussed, espe- 

 cially with regard to its religious bearing. The 

 interesting fact that the Mexican priests dis- 

 covered the very accurate coincidence between five 

 synodic periods of Venus and eight solar years is 

 mentioned incidentally. 



The second chapter is devoted to the nature 

 and origin of the Milky Way. Prof. Arrhenius 

 inclines to the view that it is a spiral nebula, and 

 suggests that it may have been formed by the 

 collision of two gaseous nebulae of immense size. 

 Recent investigations on stellar motions and their 

 relation to spectral type, and on the rotations of 

 nebulae, are discussed at considerable length. It is 

 highly creditable to the author and the publishers 

 that work published so recently as 1917 is re- 

 ferred to, though the absence of all mention of 

 the ellipsoidal theory is regrettable. 



The surface features, and especially the climatic 

 conditions, of the planets are next discussed at 

 great length and in a very interesting manner. 

 The history of the earth's atmosphere, regarded 

 as largely derived originally from volcanic gases, 

 leads to an account of the leakage of gases from 

 planetary atmospheres and the ability of the inner 

 planets to support life. Mars is declared unin- 

 habitable, as its mean temperature must be about 

 - 37° C., and even at noon on the equator it can 

 scarcely rise much above freezing-point; the avail- 

 able water supply is also exceedingly low. The 

 canals are considered to be fissures corresponding 

 with the dislocation fissures on the earth. 



Mercury and the moon are totally uninhabitable 

 on account of the absence of atmosphere. Venus, 

 on the other hand, has a dense, warm atmosphere 

 of high humidity, and "everything on it is drip- 

 ping wet." Life may therefore exist; that near 

 the equator would be of a low order on account of 

 the uniform climate and lack of need for specialisa- 

 tion ; that in higher latitudes max, however, be 

 more highly differentiated. 



A few blemishes somewhat mar a very instruc- 

 tive book. Such are the title, which is unfor- 

 tunate for a work the scope of which, except for 

 one chapter of forty-three pages, is confined to 

 tin solar system; the opening sentence, "Astro- 

 nomy occupies a rather unique position among 

 the natural sciences "; the illucid account of W. S. 

 Adams's work on p. 56; such remarks as "the 

 Original matter of the stars stands still in space " 

 (p. 55) ; " what force . . . causes the motion of 

 the Stars?" (p. 56); "Mercury lies five times 

 nearer the sun than the earth does" (p. 230) ; the 

 mention of "hydrate of chlorine" (p. 165); :mi\ 

 the reference (p. 245) to "the title-page illustra- 

 tion," which docs not exist. H. f. 



