produced ly Electricity. 409 
were found to be very great, and the quantity of iron filings that 
it attracted, was such as to form a cylinder round it of near ‘3 
the tenth of an inch in diameter. 
To ascertain whether short lengths of fine wire, steverited fi from 
fusing by being kept cool, transmitted the whole electricity of 
powerful Voltaic batteries, ‘pmade:a'second independent circuit 
from the ends of the battery with silver wires in water, so that 
the chemical decomposition of the water indicated a residuum 
of electricity in the battery. pperositts in this way, I found that 
an ineh of wire of platinum of 25, kept cool by water, left a 
great residual charge of electricity in a combination of twelve 
batteries of the same kind as those above mentioned ; and after 
making several trials, I found that it was barely adequate to dis- 
charge six batteries. 
V. Having determined that there was a Jimit to the quantity 
of. electricity which wires were capable of transmitting, it became 
easy to institute experiments on the different. conducting powers 
of different metallic ‘substances, and on the relation of this power 
to the temperature, mai ss, surface, or length of the conducting 
body, and to the cot tions of electro-magnetic action, 
: These experiments were made as nearly as possible under the 
same. circumstances, the same connecting copper wires being 
oats 1 all cases sy their diameter being ‘more. than ‘one-tenth of 
( ‘the contact being always preserved perfect ; and 
ame solutions of acid and water were employed in 
teries, and the same silver wires and broken cir- 
penal eunplayeds in the different trials; and when 
e es of gas were observed upon the negative silver wire 
circuit, it was. concluded that the metallic con- 
prea obits or the primary circuit, was adequate to the dis- 
charge of the combination. To describe more minutely all the 
precautions observed, would be tedious to those persons “who are 
accustomed to experiments with the Voltaic apparatus, aud un- 
intelligible to others; and after all, in researches of this nature, 
it is impossib!e to gain more than approximations to true results ; 
for the gas disengaged upon the plates, the different distances of 
the connecting plates, and the slight difference of time in making 
the connexions, all interfere with their perfect accuracy. 
The most remarkable general result that I obtained by these 
researches, and which I shall mention first, as it influences all the 
others, was, that the conducting power of metallic bodies var ied 
with the temperature, and was lower in some inverse ratio as 
the temperature was higher. 
Thus a wire of platinum of z4,, and three inches in length, 
when kept cool by oil, discharged the electricity of two batteries, 
Vol, 58. No, 284. Dec. 1821, 3 F or 
