212 



SCIENCE 



[N. 8. Vol. XXXIX. No. 997 



those employed with emission spectra and the 

 difficulties arise from peculiar causes. The 

 close analogy of the effects with those of 

 bright line spectra is well worked out, however, 

 and we must admire the skill shown in tracing 

 out the action of polarization of the white 

 light and varying density of the absorbing 

 vapor in altering the effects. 



In the following chapters, several branches 

 of investigation of the Zeeman effect are con- 

 sidered in turn. A short account is also given 

 of the related phenomena of magnetic rota- 

 tion in vapors and magnetic double refrac- 

 tion. The study of multiple resolutions is 

 traced, from the observation that all lines are 

 not normal triplets to the profoundly signi- 

 ficant relation of the coromensurability of the 

 components given by Eunge. Dissymmetries 

 in the resolution and a shift of the middle 

 component are features of the later study 

 which are reviewed by Zeeman. 



A chapter on solar magneto-optics simimar- 

 izes the results of the study of the magnetic 

 field of sun-spots by Hale and of his first obser- 

 vations on the general field of the sun. This is 

 followed by a chapter describing the important 

 experiments of Zeeman and Winawer on the 

 inverse effect in directions inclined to the 

 field. Undertaken because of its application 

 to the solar magnetic effects, this work has 

 been carried out with the highest skill and 

 resourcefulness. Results have been obtained 

 which undoubtedly bear closely on the solar 

 phenomena and can be applied when sun-spots 

 are again in evidence. 



The closing chapter of the monograph, on 

 the relation between magnetic resolution and 

 the chemical nature of the elements, may be 

 characterized as a statement of unsolved prob- 

 lems. In it we are made to feel how young 

 the subject of magneto-optics is, and that in 

 some directions the considerable mass of ex- 

 perimental material has served to show that a 

 connection with other departments of knowl- 

 edge exists but leaves the nature of the rela- 

 tion highly obscure. Thus, the relation be- 

 tween magnetic resolution and arrangement 

 of the lines in series is clear only for a few 

 elements having low atomic weights and few 



lines in their spectra. The fact that a series- 

 line which is double with no field may change 

 to a simple triplet in the field is an anomaly 

 which affects the whole question of the con- 

 nection with series relations. There is prob- 

 ably a fundamental relation between magnetic 

 resolution and the pressure effect, but no close 

 correspondence in detail. 



A summary of the leading features of sev- 

 eral atomic theories and a highly useful 

 bibliography, giving the entire literature ar- 

 ranged according to year of publication, close 

 a volume which will be appreciated by every 

 student of the subject. 



Arthur S. Krao 



Mt. Wilson Solar Obsebvatoet 



Mountains, their Origin, Growth and Decay, 

 By James Geikie, LL.D., F.R.S., etc^ 

 Edinburgh, Oliver and Boyd. 1913. Pp. 

 311, 80 PL, 57 Pigs, in text. 

 This volume contains in systematic form 

 the substance of various contributions made 

 by Professor Geikie during the last twenty 

 years, supplemented with much new matter.. 

 The author recognizes two classes of moun- 

 tains, original or tectonic, and subsequent or- 

 relict. 



Tectonic mountains are due to accumulation- 

 or deformation; the former includes the vari- 

 ous types of volcanoes as well as glacial and' 

 seolian hills ; all of which grow by additions to 

 the outside; the latter includes folded, dislo- 

 cation and laccolith forms, all due to crustal 

 disturbance. The study of tectonic mountains 

 occupies by far the greater part of the work, 

 which is intended to be a non-technical pres- 

 entation of the subject. Such matters as- 

 glacial action, metamorphism, types and! 

 causes of folding, structure of the Alps, origin 

 of ocean " deeps " are discussed as simply and 

 easily as though they were familiar topics of 

 every-day conversation. Certainly, this mode 

 of treatment shows that exact scientific method 

 does not require much aside from ordinary 

 language, for one knowing only the general 

 principles of physics and geology can grasp the 

 situation so as to appreciate the difficulties- 

 with which an investigator must contend as- 



