138 Analyses of Books. [Aug. 



is a sketch of the splendid chemical discoveries to which the 

 galvanic battery gave occasion, and for which we are almost 

 entirely indebted to the sagacity and industry of Sir H. Davy. 



Our author terminates his historical sketch with De Luc's 

 discovery of the galvanic column, and with the facts which Mr. 

 Children was enabled to ascertain by his experiments with his 

 magnificent battery, composed of pairs of plates, each six feet in 

 length. 



The theory of the galvanic battery has hardly kept pace with 

 the discoveries which have originated from its use. Three 

 different theories have been proposed. 1. That the galvanic pile 

 is entirely electrical. 2. That it is entirely chemical. 3. That 

 the electricity produces the phenomena, but is itself evolved by 

 the chemical action. The first of these theories was broached 

 by Volta, the second by Donovan, the third by Wollaston, but 

 developed by Dr. Bostock. Our author considers the last of 

 these theories as the true one, though he admits that the subject 

 requires further investigation. 



As it has been ascertained by unequivocal experiments that 

 the galvanic pile never acts unless when one of the metals com- 

 posing it is oxidized, and that its energy only continues as long 

 as the oxidizing process is going on, it seems evidently to 

 follow that Volta's theory is imperfect, unless it be maintained 

 that a current of electricity cannot exist without occasioning 

 chemical decompositions, of which at present we have no 

 evidence. 



The most cursory attention to the galvanic pile is sufficient to 

 demonstrate that it never acts except the circle be completed ; 

 that is, unless there be a current of electricity. This seems 

 sufficient to set aside Donovan's theory, unless he can show that 

 a current of chemical affinity is precisely analogous to a current 

 of electricity. 



It cannot then, I think, be doubted, that both chemical decom- 

 positions and a current of electricity are necessary to constitute 

 the galvanic pile ; but no one has hitherto succeeded in showing, 

 in a satisfactory manner, how the chemical decompositions evolve 

 the electricity, nor how the two sets of conductors, constituting 

 the galvanic pile, occasion a current of electricity in one direc- 

 tion, even supposing its evolution to be taken for granted; or to 

 be supposed accounted for by the observations of Mr. Cuthbert- 

 son. Dr. Bostock's hypothesis, that the current is occasioned 

 by the combination of the electricity with hydrogen, cannot be 

 maintained ; for when dilute nitric acid is employed to fill the 

 cells of a galvanic battery, it is not hydrogen that is evolved at 

 the copper plates, but nitrous gas, as I have very often observed. 

 Upon the whole, a satisfactory theory of galvanism is still want- 

 ing. The present little work will be exceedingly useful to any 

 person who shall hereafter undertake to supply this desideratum 

 in science. It is, therefore, a performance for which men of 

 science are under obligations to the author. 



