Chemistry and Physics. 255 



number of organic substances in the infra red. His results show 

 that all compounds in which the radical CH 3 enters have a maxi- 

 mum of absorption at wave-length ^ = 3'45,m and a second be- 

 tween 8 and 9/u. The fluids which contain oxygen absorbed 

 wares from 10 to 20 ; «. The chlorine compounds show a certain 

 correspondence at definite points of the spectrum. — Beiblatter 

 Ann. der Physik und Chemie, No. I, 1893, p. 34. j. t. 



9. The Opticcd Indicatrix and the Transmission of Light in 

 Crystals, bj L. Fletcher. 112 pp. 8vo. London, 1892 (Henry 

 Frowde, Oxford University Press Warehouse). — To the student 

 who is bewildered by the conflict of optical theories, this treatise 

 will supply a real want in furnishing those relations which can be 

 verified by experiment, unincumbered by any dynamical theory. 

 The deductions are generally based on simple geometrical con- 

 siderations relating to the ellipsoid which the author calls the 

 Indicatrix, analytical formula? being added for those whose taste 

 requires them, and for the purposes of numerical calculation. 

 The historical notes, though brief, are valuable, and may give a 

 better idea of the actual discovery of the wave-surface, than 

 might be obtained by the reading of some classical memoirs, 

 while the references to optical theories are entirely free from 

 parti pris. The standpoint of the author is in fact that of the 

 crystallographer, interested in the optical behavior of crystals, 

 rather than that of the physicist to whom the vital question 

 relates to the essential nature of light. 



10. A Text-book of Physics, largely experimental, by Edwin 

 H. Hall and Joseph Y. Bergen, Jr. 388 pp. 12mo. New York, 

 1892 (Henry Holt and Company). — This text-book is to a con- 

 siderable extent based upon the Harvard College descriptive list 

 of elementary physical experiments (first issued in 1887) called 

 out by the requirement, made in 1886, of laboratory work in 

 Physics. The experiments are well selected and with the guid- 

 ance of a competent teacher should produce good results. As 

 the authors remark, however, the book is designed " to guide the 

 student in his thinking not to relieve him from the necessity of 

 thinking ;" the danger of early laboratory work seems to be that 

 it may bring the mere experiment before the student's mind more 

 prominently than the physical law which it illustrates. This 

 difficulty the author seems to have attempted to avoid so far as 

 this can be done by written words. 



1 1. Theoretical Mechanics, a Class book for the Elementary 

 Stage of the Science and Art Department, by J. Spencer. 242 pp. 

 12mo. London, 1892 (Percival and Co.). — The author has added 

 another to his series of successful elementary text-books, several 

 of which have been before noticed in this Journal. The princi- 

 ples are clearly stated throughout and their application well illus- 

 trated by numerical examples. 



