674 SCIENCE PROGRESS 



for preventing their ruin, will be carried out so that they may long serve as a 



record of an interesting phase in the history of Hindu astronomy. The numerous 



reproductions of metal and masonry instruments are excellent and deserve high 



praise. 



H. S. J. 



PHYSICS 



Les Progres de la Physique Moleculaire : Conferences faites en 1913-14 par 

 Mme. P. Curie, J. Becquerel, M. de Broglie, A. Cotton, Ch. Fabry, 

 P. Langevin, Ch. Mauguin, H. Mouton. [Pp. 244, with plates and 

 figures.] (Paris : Gauthier-Villars et Cie., 1914.) 



This volume is the second of the series of physical memoirs published by the 

 Physical Society of France. Publication has been considerably delayed by the 

 war, and although the volume is dated 1914 it has only recently appeared. It 

 contains seven separate memoirs, each of which is in the nature of a review of 

 recent progress in the branch of physics under discussion. The whole series 

 caken together provide a useful summary of the most important advances in 

 physics in the few years preceding the year 1914. 



An excellent memoir on "La Physique du Discontinu" is contributed by 

 P. Langevin. Perhaps the most important change in physical ideas during recent 

 years has been the manner in which the fundamental notion of discontinuity has 

 penetrated all its branches. This has necessitated a modification of the mathe- 

 matical treatment of the subject : the differential and integral calculus inherently 

 involve the conception of continuity, and have had to be replaced by the statistical 

 methods and calculus of probabilities, introduced by Maxwell and developed by 

 Boltzmann. In this article Langevin discusses several problems in probabilities 

 and shows how various physical problems can be reduced to one or other of them. 

 The physical illustrations are taken from many branches of physics, and many 

 important results are derived. The memoir is written with admirable terseness 

 and lucidity, and its publication in book form, so as to procure a much wider 

 circulation, is much to be desired. 



A somewhat brief memoir on " Les Progres de nos Connaissances concernant 

 les Rayons de Rontgen " is written by M. de Broglie. This deals mainly with the 

 properties of secondary Rontgen rays and with the phenomena of diffraction of 

 Rontgen rays. Considerable progress has naturally been made in these directions 

 since the memoir was written. 



M. Mauguin has given an account of the curious phenomenon of liquid 

 crystals, and of their properties. He gives strong evidence as to the reality of 

 their crystalline nature, and points out the interesting fact that they are all 

 uniaxial. Hypotheses to account for this are discussed. 



Mme. Curie has contributed a memoir on " Les Radio-Elements et leur 

 Classification." Two important rules are advanced which govern the position of 

 the radioactive elements in the periodic system. They may be combined thus : 

 when a radioactive transformation takes place with (without) emission of a-rays, 

 the resulting element whose atomic weight is four units less than (the same as) 

 the parent substance, is displaced with reference to the latter by two (one) 

 columns in the direction of decreasing (increasing) atomic weights. It is also 

 shown that the radio-elements form groups of bodies with the same chemical and 

 electrochemical properties, each group playing the role in the periodic system of 

 a single element. The constitution of the various groups is then studied. 



H. Mouton deals with the subject of" Birefringence Magnetique des Liquides 



