Intelligence and Miscellaneous Articles, 155 



such diiFerent conditions of depth, mineral composition of sea-bottom, 

 &c. A certain number of peculiar species must necessarily result 

 from such different conditions, but the author considered it pro- 

 bable that the same causfes would lead to the existence of such 

 marked varieties as might, viewing each area separately and inde- 

 pendently, cause some varieties to assume the permanence and 

 importance of specific differences. Until the exact synchronism of 

 any deposit is established, the Palaeontologist cannot always fully 

 take these causes into consideration, and many admirable monographs 

 on Tertiary fossils have necessarily been fouiinled, in a great measure, 

 upon the differences actually app'arent, and persistent in the several 

 areas. 



Mr. Prestwich stated that it was hi^ intention to continue this 

 inquiry at a future period, and to examine into the correlation of the 

 curious and interesting freshwater and fluviatile series overlying the 

 Barton clay on the Hampshire coast and in the Isle of Wight. 



XXII. Intelligence and Miscellaneous Articles. 



ON THE HEAT ABSORBED IN CHEHICAL DECOMPOSITIONS. 



To the Editors of the Philosophical Maga-zitbe and Journal. 

 Gentlemen, Manchester, July 4, 1856. 



IN your Number for this month, p. 74, Dr. Woods mis-states the 

 results I arrived at fifteen years ago, and endeavours to support 

 his own claims as an original discoverer by setting up one portion of 

 my papers in contradiction to another. He says that when I caused the 

 current to pass through an electrolyte, I did not find the same law to 

 exist as when it passed through a metallic conductor. On the con- 

 trary, he will find in my paper ^hil. Mag. Oct. 1841, pp. 270-274) the 

 account of seven experiments, by which it was proved, that in an elec- 

 trolytic cell the heat is evolved proportionally to the resistance to con- 

 duction and the square of the current, — thesamelawwhichlhadshown 

 to exist in the case of a metallic wire and in that of the cell of a bat- 

 tery. Also at p. 275, he will see a general rule expressed as follows : — 

 " When any voltaic arrangement, whether simple or compound, passes 

 a current of electricity through any substance, whether an electrolyte 

 or not, the total voltaic heat which is generated in any time is pro- 

 portional to the number of atoms which are electrolyzed in each cell 

 of the circuit, multi] liedby the virtual intensity of the battery." A 

 foot-note to the word ' virtual ' explains its meaning by saying, that 

 *' If a decomposing cell be in the circuit, the virtual intensity of the 

 battery is reduced in proportion to its resistance to electrolyzation." 

 I think that the meaning of the above proposition is sufficiently clear, 

 but will nevertheless illustrate it by two examples. Suppose, first, 

 we take a voltaic battery of 20 iron zinc pairs, and connect its ter- 

 minals by a metallic wire. After a ceYtain interval of time, we find 

 100 atoms or chemical equivalents of zinc dissolved in each cell of 



