and on the Mechanical Value of Heat. 



439 



Another experiment, conducted in precisely the same man- 

 ner as the above, gave, per degree of heat, a mechanical power 

 capable of raising 587 lbs. to the height of one foot. 



As the preceding experiments are somewhat complicated, 

 and therefore subject to the accumulation of small errors of 

 observation, I thought it would be desirable to execute some 

 of a more simple character. For this purpose I determined 

 upon an arrangement in which the whole of the heat would 

 be evolved in the revolving tube. 



The iron cylinder used in previous experiments was placed 

 in an electrotype apparatus constructed in such a manner as 

 to render every part of it equally exposed to the voltaic action. 

 In four days 1 1 oz. of copper were deposited in a hard com- 

 pact stratum. The ends of the cylinder were then filed until 

 the iron just appeared. Thus I had a cylinder of iron imme- 

 diately surrounded by a hollow cylinder of pure copper nearly 

 one-eighth of an inch thick. This was placed in the centre of 

 a new revolving tube fitted up in precisely the same manner as 

 the former one, which had been accidentally broken, and sur- 

 rounded with 11^ oz. of water. I give the following series of 

 experiments in which the above was rotated between the poles 

 of the large electro-magnet excited by ten cells arranged in a 

 series of five double pairs, a galvanometer being included in 

 the circuit to indicate the electric force to which the electro- 

 magnet was exposed. 



No. 16. 



