Notices respecting New Boohs. 197 



general problem of photographic reproduction with sug- 

 gestions for enhancing gradation originally invisible " 

 (Phil. Mag. xxii. p. 734 (1911)), reprinted (British Journal 

 of Photography, lviii. p. 994 (1911)). In this paper Lord 

 Rayleigh certainly goes to the root of the matter so far as 

 the matching of plates is concerned, but does not leave the 

 problem in a form suitable for practice. In particular, 

 some of the assumptions made in the typical cases taken do 

 not fit in with practical aims. For example, there is no 

 object in making the gradation of the negative the same as 

 the positive. The only condition which seems to us useful 

 is that the gradation in the issuing light (I) shall be the 

 same as that from the original source (E^. This is the 

 condition which we have taken as fundamental. 



XV. Notices respecting New Books. 



A System of Physical Chemistry. By William C. M c C. Lewis, 

 Professor of Physical Chemistry, University of Liverpool. 

 Longmans, G-reen & Co. In 3 volumes. (Second Edition.) 



^TVHE first edition of this work is, of course, well known to all 

 -■- students of physical chemistry. The general arrangement 

 of the matter in the new edition is similar to that of the first, 

 but the large amount of new material which has been incorporated 

 has made a third volume necessary. The first volume deals with 

 the kinetic theory, and we are introduced at once to the very 

 recent work of Perrin, Svedberg, Wilson, and Millikan, on the 

 physical properties of molecules, the Brow T nian movement of 

 small particles suspended in liquids and gases, and their behaviour 

 in electric and gravitational fields. Among the new additions to 

 Volume I. maybe mentioned: The study of the arrangement of 

 the atoms in crystals by means of X rays, as developed by Laue, 

 Bragg and others, the dissociation of the vapour of ammonium 

 chloride in the light of recent experiments, the dual theory of 

 homogeneous catalysis, the " displacement effect " (a term suggested 

 by the author for effects produced by gradually replacing one 

 reactant by another), and Langmuir's very recent work on hetero- 

 geneous reaction velocity, condensation and evaporation, chemical 

 theory of surface tension and the general mechanism of surface 

 forces. The volume contains an enormous amount of information 

 of great interest to the general reader, and should be in the 

 library of everyone interested in the recent developments of 

 science. The subject of suspensions, emulsions ami colloidal 

 solutions is very fully treated, and is of especial interest in that 

 numerous applications of the theories are made to matters of 



