Metallic Bodies by Voltaic Electricity. 213 



mentioned *, namely, that the excitation of heat occasions the 

 imperfection of the conducting power, seems, to a very great ex- 

 tent, extremely probable, as may be seen in the following expe- 

 riments : 



(c.) Having excited, somewhat powerfully, a large electro-mag- 

 netic battery (B. Figs. 3-4), of the cylindrical form, and contain- 

 ing about two square feet of zinc, with double copper ; the vol- 

 taic action was transmitted through the electrometer E, as in the 

 previous experiments, by means of large copper- wires connect- 

 ing the zinc and copper sides. In order to exemplify the in- 

 fluence of heat in decreasing the conducting power, about six 

 inches of the circuit mn, Fig. 3, was made up of smaller wire, of 

 about the ^ O th of an inch in diameter, and to this wire, the flame 

 of a spirit-lamp was applied, when the fluid in the electrometer E, 

 had attained its greatest height on the scale ; the result was, 

 that the fluid began to descend, as the wire m n became heated, 

 and again recovered its former point of elevation on removing 

 the lamp -f. 



(d) A somewhat similar result was obtained, in substituting for 

 the wire m n, another wire of the same dimensions, but of worse 

 conducting power ; in which case, the effect on the electrometer 

 E was considerably diminished. 



(e) When the wire m n was kept cool by evaporating a little 

 ether from its surface, the effect on the electrometer was greatly 

 increased. 



(f) Similar results were obtained, when, instead of allowing 

 the wire mn to form a part of the circuit, as in Fig. 3, it was 

 made to connect the contact cups of the battery. In this case, 



* Phil. Transactions for 1821, p. 438. 



f This experiment with the electrometer had been previously tried by Mr 

 JONATHAN HEAIIDEK, of this place, to whose friendly assistance I have been occa- 

 sionally much indebted, in the progress of these inquiries. 



VOL. XII. PART I. EC 



