1854.] OF THE ROYAL INSTITUTION. 351 
an inch in diameter, be insulated in the air, ELE CANS 
having its end m a metal ball; its end e if ‘ 
connected with the earth, and the parts near | 
m and e brought within half an inch of each 
other, as at s; then an ordinary Leyden jar 
being charged sufficiently, its ‘outside con- 
nected with e and its inside with m, will give 
a charge to the wire, which instead of tra- 
velling wholly through it, though it be so 
excellent a conductor, will pass in large pro- 
portion through the air at s, as a bright * 
spark: for with such a length of wire, the Ss 
resistance in it is accumulated until it becomes 
as much, or perhaps even more, than that of 
the air, for electricity of such high intensity. mit. 
Admitting that such and similar experiments 4 
shew that conduction through a wire is preceded by the act of 
induction (1338), then all the phenomena presented by the sub- 
merged or subterranean wires are explained ; and in their explanation 
confirm as I think, the principles given. After Mr. Wheatstone 
had, in 1834, measured the velocity of a wave of electricity through 
a copper wire, and given it as 288,000 miles in a second, I said, in 
1838, upon the strength of these principles (1333,) “that the 
velocity of discharge through the same wire may be greatly varied, 
by attending to the circumstances which cause variations of 
discharge through spermaceti or sulphur. Thus, for instance, it 
must vary with the tension or intensity of the first urging force, 
which tension is charge and induction. So if the two ends of 
the wire, in Professor Wheatstone’s experiment, were immediately 
connected with two large insulated metallic surfaces exposed to 
the air, so that the primary act of induction, after making the 
contact for discharge, might be in part removed from the internal 
portion of the wire at the first instant, and disposed for the moment 
on its surface jointly with the air and surrounding conductors, 
then I venture to anticipate, that the middle spark would be more 
retarded than before: and if these two plates were the inner and 
outer coating of a large jar, or a Leyden battery, then the retar- 
dation of that spark would be still greater.” Now this is precisely 
the case of the submerged or subterraneous wires, except that 
instead of carrying their surfaces towards the inducteous coatings 
(1483), the latter are brought near the former; in both cases the 
induction consequent upon charge, instead of being exerted almost 
entirely at the moment within the wire, is to a very large extent 
determined externally ; and so the discharge or conduction being 
caused by a lower tension, therefore requires a longer time. 
Hence, the reason why, with 1500 miles of subterraneous wire, 
the wave was two seconds in passing from end to end; whilst 
with the same length of air wire, the time was almost inappre- 
ciable. 
