416 Notices respecting Neiu Books, 



into an ozonizer (Plate XT. b). Less efficient still is the 

 arrangement whereby the oxidizable nitrogen is mixed with 

 ozonized air in a mixing chamber a few feet away from the 

 discharge apparatus (Plate XI. a). The slight, but clearly 

 marked gradation in the first three exposures of Plate XL 

 affords unmistakable evidence of the instability of the oxidi- 

 zable variety of nitrogen, which appears to revert in the 

 course of a few seconds to a form in which it can no longer 

 be oxidized either by oxygen or by ozone. 



The observations now described are probably of importance 

 in connexion with the technical fixation of nitrogen. It is 

 not unreasonable to suggest that, since the whole of the 

 oxides of nitrogen must be produced by the union of dis- 

 rupted molecules of nitrogen with disrupted molecules of 

 oxygen, the most important feature of the process may be to 

 generate the oxidizable variety of nitrogen and then to 

 provide a supply of atomic or of ozonized oxygen to oxidize 

 it before it reverts to the ordinary inactive form. 



As a point of contrast it should be noticed tha t Strutt's 

 chemically active nitrogen is not oxidizable by oz me under 

 the conditions of his experiments. 



The author is indebted to Mr. Henry Simon, of Manchester, 

 for permission to publish an account of these experiments. 



XLIX. Notices respecting New Books. 

 Photoelectricity. By A. Ll. Hughes, D.Sc, B.A. 

 Pp. viii +144. Cambridge University Press. 1914. 

 r PHIS book deals principally with the emission of electrons from 

 -■- solids, liquids, and gases under the influence of light, and is 

 a valuable addition to the Cambridge Physical Series. The most 

 interesting questions at issue relate to the velocities and the 

 numbers of the emitted electrons, and the way these quantities 

 depend on the frequency and the intensity of the exciting light, 

 and on the nature of the emitting substances. The treatment is 

 ftot limited to these questions, but includes a number of related 

 phenomena. The part dealing with the relation between fluores- 

 cence, phosphorescence, and photoelectric emission is particularly 

 satisfactory. 



The subject is of especial interest at present on account of the 

 light it throws on the so-called quantum theories. Professor 

 Hughes has made many valuable contributions towards its recent 

 development, and his opinions on the more controversial points 

 will be read with interest. The book bears evidence that it is 

 written by one who is familiar with the experimental difficulties 

 W'hich beset this line of investigation. It will be welcomed by all 

 who are interested in modern experimental and theoretical physics. 



