98 ON THE HEAT EVOLVED DURING 
diameter, consisting of 200 turns of well covered 
copper wire of 2, in. diameter. As the resistance 
of a voltaic pair, consisting of three inch plates, 
is seldom more than equal to that of a yard of 
such wire, the galvanometer could now be depend- 
ed upon as an indicator of the intensity of differ- 
ent arrangements, particularly by taking care to 
make their resistances as nearly equal to one 
another as possible. In this way, calling the 
intensity of Daniell’s cell unity, I found the inten- 
sity of Mr. Grove’s arrangement, consisting of 
platinum in nitric acid and amalgamated zinc in 
dilute sulphuric acid, to be 1°732; and that of 
Mr. Smee’s arrangement of platinized platinum 
and amalgamated zine in dilute sulphuric acid 
(avoiding the effects of immersion*) to be 0°731: 
also the intensities of similar arrangements, with 
ron as the positive metal, to be respectively 1°14 
and 0:149. 
Now on account of the extreme facility with 
which oxygen parts from nitric acid, there can be 
no doubt that the intensity of the above arrange- 
* Phil. Mag. 1842, Vol. 20, p. 105. Becquerel was, I be- 
lieve, the first who referred the great intensity of a pair 
at the moment of its immersion to the reaction of the air ad- 
hering to the negative plate. 
