2G0 Mr. J. P. Joule on the Heat evolved by Metallic 



that they have been formed by the upheaval of shoals, depo- 

 sited where currents met. These phenomena, it is very pro- 

 bable, are connected in their origin with the same causes 

 which have produced the remarkable bar of sandstone off 

 Pernambuco. The town of Pernambuco stands on a low 

 narrow islet and on a long spit of sand, in front of a very low 

 shore, which is bounded in the distance by a semicircle of 

 hills. By digging at low water near the town the sand is 

 found consolidated into a sandstone, similar to that of the 

 breakwater, but containing many more shells. If, then, the 

 interior of a long sandy beach in one part, and in another 

 the nucleus of a bar or spit extending in front of a bay be- 

 came consolidated, a small change, probably of level, but per- 

 haps simply in the direction of the currents, might give rise, 

 by washing away the loose sand, to a structure like that in 

 front of the town of Pernambuco, and along the coast south- 

 ward of it; but without the protection afforded by the success- 

 ive growth of organic beings, its duration would be short, if 

 indeed it were not destroyed before being completely exhi- 

 bited. 



XXXVIII. On the Heat evolved by Metallic Conductors of 

 Electricity, and in the Cells of a Battery during Electrolysis. 

 By James Pkescott Joule, Esq/* 



1. npHERE are few facts in science more interesting than 

 J- those which establish a connexion between heat and 

 electricity. Their value, indeed, cannot be estimated rightly, 

 until we obtain a complete knowledge of the grand agents 

 upon which they shed so much light. I have hoped, there- 

 fore, that the results of my careful investigation on the heat 

 produced by voltaic action, are of sufficient interest to justify 

 me in laying them before the Royal Society. 



Chap. I. — Heat evolved by Metallic Conductors. 



2. It is well known that the facility with which a metallic 

 wire is heated by the voltaic current is in inverse proportion 

 to its conducting power, and it is generally believed that this 

 proportion is exact ; nevertheless I wished to ascertain the 

 iact for my own satisfaction, and especially as it was of the 

 utmost importance to know whether resistance to conduction 

 is the sole cause of the heating effects. The detail, therefore, 

 of some experiments confirmatory of the law*, in addition to 

 those already recorded in the pages of science, will not, I 

 hope, be deemed superfluous. 



* Communicated by the Author. 



