Chemistry and Physics. 431 



in which the matter was contained, remained white. Only at long 

 intervals were further steps made. Thirty years later Beccaria 

 made the observation that the coloring of silver chloride was due 

 to the action of light and not as previously supposed, to that of 

 the air. In weighing the relative claims of Nicephore Niepce and 

 of Daguerre to the actual discovery of photography the author is 

 disposed to believe that the former has received too little and the 

 latter more than his due share of the honor. The discoveries 

 which rapidly followed after this are next described and the 

 author has evidently devoted much care and thought to the pre- 

 sentation as well of the theoretical views as of the practical 

 processes which have been brought forward up to the present 

 time. 



The book seems to deserve a translation into English, m. c. l. 



11. Die Elektrischen Verbrauchsmesser von Etienne de 

 Fodor. 219 pp. 12mo. Vienna, 1891. — Electro-technical Library, 

 vol. xliii (A. Hartleben). The electro-technical library, the 

 earlier issues of which have been noticed in the Journal, has 

 grown to upwards of 40 volumes covering a wide range of topics. 

 It would be difficult to find elsewhere so much direct practical 

 information on subjects dealing with the technical application of 

 Electricity, as is compressed into these little volumes. The 

 present issue takes up the subject of Electric meters and with 

 great fullness gives the many forms that have been devised, from 

 the earliest kinds first described to those now found most practi- 

 cally useful. The forms described are so numerous that the 

 account of each is brief, but the abundance of illustrations adds 

 much to the completeness of the treatment. 



12. Das Totalreflectometer unci das Rej Tactometer fur Chemiker, 

 ihrer Verwendung in der Krystalloptik und zur Untersuchung 

 der Lichtbrechung von Flussigkeiten von Dr. C. Pulfrich. 144 

 pp. 8vo, with 4 plates. Leipzig, 1890 ( Wm. Engelmann). — This 

 volume contains a thorough discussion of the theory and practi- 

 cal use of the new form of totalreflectometer, first described by 

 the author in 1887 ( Wied. Ann., vol. xxx, p. 193). The method 

 consists, in a word, in determining the critical angle for the light- 

 ray which has passed from below into a glass cylinder and suf- 

 fered total reflection from the surface of the substance under 

 examination placed upon the plane surface of the cylinder. The 

 required refractive index is given by the equation n = /y/N 2 _ sin 2 7 

 where N is the index for the glass and i the angle of emergence. 

 By using different kinds of glass from N = 1*95 to 1*60, refrac- 

 tive indices from 1*675 to 1*249 may be determined. The method 

 is easy of application and, as shown by measurements by the 

 author and others by Miihlheims, capable of giving accurate re- 

 sults. A special chapter describes the modification of the instru- 

 ment as designed for the use of chemists in the measurement of 

 refractive indices of solutions. 



13. Appleton^s School Physics; embracing the results of the 

 most recent researches in the several departments of Natural 



