Chemistry and Physics. 453 



very distinct; whilst with less rarefaction, these two bodies 

 transmit the rays in about the same degree (Nature, Oct. 29, 

 1896). It is thought, however, by certain observers that the 

 bones become phosphorescent under certain energy of excita- 

 tion, and therefore the field of view exhibits less contrasts. It 

 has been discovered that fluorescent screens in order to be of use 

 should not be phosphorescent : for this residual phosptiorescence 

 renders the contrast between bones and flesh less evident. A 

 determination of the wave-length of the X-rays has been made 

 by L. Fomm (Ann. dcr Physik und Chemie, No. 10, 1896, p. 350). 

 He obtained through a slit evidences of interference phenomena 

 similar to those observed in the case of ordinary short waves of 

 light, and by means of a formula given by Dr. V. Lommel for 

 the case of such interference phenomena he obtained the wave 

 length X — 0-000014'"". This wave length is at least fifteen times 

 smaller than the shortest hitherto observed wave length of ultra 

 violet light. A. Winkelman and K. Straubel (Ann. der Physik 

 und Chemie, No. 10, 1896, p. 324) call attention to the remarkable 

 sensitiveness of fluorspar to the X-rays. The portion of a photo- 

 graphic plate beneath a plate of this mineral which is exposed to 

 the X-rays becomes as black as if it were submitted to direct 

 daylight. Unfortunately it is impossible to procure large plates 

 of fluorspar to cover photographic plates. When the mineral is 

 pulverized and sifted on a sensitive plate it does not seem to act 

 as well as when it is in moderate-sized pieces. The use, however, 

 of large pieces mottles the sensitive plates and destroys the defi- 

 nition of objects photographed on it. j. t. 



13, The Frincij^les of the Transformer^' by Frp:derick Bedell, 

 Ph.D. xii-f404 pp. New York, 1896 (The Macmillan Company). — 

 This book is, in a measure, a continuation of Bedell and Crehore's 

 " Alternate Currents," and is similar to it in general aim and 

 methods of treatment. The same clearness of reasoning and 

 lucidity of style which have justly rendered the previous work 

 ])opular among students are apparent in this volume also. 

 Occasionally, however, the desire for clearness in demonstration 

 seems to have led the author almost to the verge of prolixity; 

 for example, it is difficult to see the utility of such minute detail 

 in the treatment of the general equations of the transformer in 

 Chapter XI; it can hardly make the subject intelligible to those 

 readers who have no acquaintance with determinants or elemen- 

 tary differential equations, and- is, on the other hand, scarcely 

 necessary lor those whose mathematical studies have included 

 these subjects. 



A dual method of treatment is adopted, many of the problems 

 being solved by analytical treatment, and also graphically by 

 means of the polar diagram. In the first twelve chapters the 

 theory of the transformer with constant coefficients of induction 

 is gradually developed with greater and greater generality ; then 

 follow several special problems, and chapters on design and con- 

 struction, experimental diagrams and transformer testing. The 



