Chemistry and Physics. 467 



(5.) That by observing the fluorescence by transparency as 

 Lubarsch has done, the proportion of the rays most absorbed is 

 strongly diminished. 



(6.) That it is, on the contrary, as great as possible when, the 

 observation being effected on the side of the incident rays, the 



"' 7H ' 



All these conclusions follow naturally from the first proposition 



and seem to involve only very natural hypotb 



This theory demands nothing but that the law of Stokefl shall 

 be in general correct. It explains, on the contrary, very well the 

 disagreement of the experiments of Lommel, made under condi- 

 tions theoretically more favorable than those of his opponents. — 

 Pogg. Ann., clx, 75, Joum. de Phys., vi, 126. e. c. p. 



Electricity and the Electric Telegraph ; by Geo. B. Pbes- 

 — New York. 1877. 

 j Mr. Prescott, is a 

 most important contribution to scientific literature, honorable 

 alike to the learning and industry of the author. It is a compre- 

 hensive review of the application of electrical principles to tele- 

 graphy. It discusses with sufficient thoroughness the laws of 

 electrical resistance and measurement; the determination of vol- 

 taic constants; the laws of electro-magnetism ; of the measurement 

 of electro-motive force ; of galvanic polarization and the applica- 

 tion of these and other principles to telegraphic circuits and land 

 lines ; the phenomena of charge and discharge on land lines and 

 underground lines ; submarine cables ; electrostatic induction on 

 telegraph lines; the phenomena of charge in submarine cables; 

 coefficient of charge in submarine and land lines ; duration of the 

 variable state when the extremity of the line is to earth, and 



ne required to produce a signal ; tne 

 earth a reservoir of electricity, and its electrical resistance. These 

 topics fill nearly half (415 pages) of the volume; the remainder is 

 occupied with a historical notice of experimental telegraphs of the 

 American and Europe 

 other systems and instruments, illustrated by very beautiful, 



original wood-cuts. The discoveries and imp] 



years, especially the duplex and quadruplex modes of transmission, 



and the improved type printing apparatus, which, as the author 



says, have in America almost revolutionized the telegraj 



are now for the first time illustrated with a completness worthy 



of the importance of the subject. The harmonic teleg 



B are also described and illustrated. Mr. Pre> 

 is prepared with great care, giving to each investigator and 

 inventor just consideration : and while it is full in its technical 

 detail it is also thorough in its scientific accuracy, qualities rarely 

 combined, and worthy of the electrician of one of the most widely 

 extended telegraphic organizations in existence. 



