produced by electricity. 435 
from these experiments, must be some hundreds of thousand 
times less than those of the worst metallic conductors. 
A piece of well-burnt compact box-wood charcoal was 
placed in the circuit, being -j— • of an inch wide by thick, 
and connected with large surfaces of platinum. It was found 
that 1 inch and carried off the same quantity of elec- 
tricity as 6 inches of wire of platinum of 
VII. I made some experiments with the hope of ascertaining 
the exact change of ratio of the conducting powers dependent 
upon the change of the intensity and quantity of electricity ; 
but I did not succeed in gaining any other than the general 
result, that the higher the intensity of the electricity, the 
less difficulty it had in passing through bad conductors ; and 
several remarkable phenomena depend upon this circum- 
stance. 
Thus, in a battery where the quantity of the electricity is 
very great and the intensity very low, such as one composed 
of plates of zinc and copper, so arranged as to act only as 
single plates of from 20 to 30 feet of surface each, and 
charged by a weak mixture of acid and water. Charcoal 
made to touch only in a few points, is almost as much an in- 
sulating body as water, and cannot be ignited, nor can wires 
of platinum be heated when their diameter is less than of 
an inch, and their length three or four feet; and a foot of 
platinum wire of ~ is scarcely heated by such a battery, 
whilst the same length of silver wire of the same diameter is 
made red hot; and the same lengths of thicker wires of 
platinum or iron are intensely heated. 
The heat produced where electricity of considerable intern- 
mdcccxxi. 3 K 
