Chemistry and Physics. 389 



union of the original work with van't Hoff's "Dix Annees dans 

 l'Histoire d'une Theorie." The central figure in the new theory 

 — suggested by Le Bel as well as by the present author — is the 

 asymmetric carbon atom. To the law of the quadrivalence of 

 carbon, announced by Kekule, van't Hoff added the hypothesis 

 that the four valences are directed toward the corners of a tetra- 

 hedron at the center of which is the carbon atom. The two 

 isomers of Pasteur, of opposite rotatory power, were explained 

 by means of this tetrahedron and its image, the isomerism disap- 

 pearing when the two groups become identical, through the 

 resulting symmetry and identity of the two tetrahedra. Thus 

 originated the subject of stereochemistry, now so firmly fixed in 

 the science. Even the little remaining opposition to it is directed, 

 as Wislicenus says, against the ultimate basis — against the atomic 

 hypothesis itself — and does not deny that the doctrine of atomic 

 arrangement in three dimensions is a logical and necessary stage, 

 perhaps the final stage, in the chemical theory of atoms. " It has 

 already effected to the full all that can be effected by any theory ; 

 for it has brought into organic connection with the fundamental 

 theories of chemistry facts which were before incomprehensible 

 and apparently isolated and has enabled us to explain them from 

 these theories in the simplest way. By propounding to us new 

 problems the hypothesis has stimulated empirical investigation on 

 all sides ; it has caused a vast accumulation of facts, has led to 

 the discovery of new methods of observation, has become amen- 

 able to the test of experiment and has at the same time started 

 in our science a movement full of significance — in a certain sense 

 indeed a new epoch." In the new edition a section on nitrogen 

 derivatives has been added ; in the part devoted to carbon the 

 greatly increased number of facts has been taken into account, 

 and special attention has been given to the amount of rotation of 

 active bodies ; thus making it a reference book at once for stereo- 

 chemistry and optical activity. The translation is an excellent 

 one, as was to be expected from the well known ability ol Dr. 

 Eiloart in this direction. g. f. b. 



7. A College Course of Laboratory Experiments in General 

 Physics ; by Samuel W. Stratton and Robert H. Millikan, 

 of the University of Chicago. 8vo, pp. iv, 100. Chicago, 1898. 

 (University of Chicago Press.) — This laboratory manual is 

 designed for the students of the Junior College Courses in 

 Physics in the University of Chicago. " The aim has been to 

 select and devise a set of experiments calculated, first to give an 

 acquaintance with the methods and a view of the field of Experi- 

 mental Physics such as is requisite to a liberal education ; and 

 second to train the student to accurate observation, skilful 

 manipulation and logical interpretation of observations." It 

 appears to us that this aim has been realized. Within this hun- 

 dred pages fifty-three experiments have been described, each 

 excellent in character, clearly and succinctly stated, requiring the 

 use of accurate and simple apparatus, and so performed as to lead 



