* 
32 Law of the Induction of an Electric Current upon itself. 
ness with which resistance to conduction is felt at the surface, the 
quantity actually developed in proportion to the mass very near 
the surface, would be extremely great in comparison with the 
quantities developed at greater depths, and this tendency of the 
initial current to the surface does certainly offer some analogy to 
the accumulation of statical electricity at the surface, though with 
the difference that the great proportion of the current does, not- 
withstanding, take the interior of the conductor. One tenth only 
f the whole initial development belongs to the external shell 
equal in thickness to the two hundredth part of the radius, which 
would include a hundredth of the mass nearly. 
22. But this thin shell would, nevertheless, conduct ten times 
its share of the current fninus the allowance to be made for re- 
away by the metal within, it can hardly be considered a very se- 
' 
pe 
rious objection to our conclusions if no instance has yet been ad- 
duced of a lightning rod or conducting wire, having its mere sur 
face melted away, especially in the absence, so far as I am in 
formed, of any experiments specially directed to that point. 
23. Asa test of the conclusions I have ventured to put forth, 
it might be proposed to coat a conducting wire with a thin sheet 
of the same, or a more refractory metal, separated from the main 
wire, except at the ends, by a bad conductor of heat, and to dis- — 
charge through the whole a heavy electric battery. Ihave essay- 
ed such an experiment but find my small electrical machine and 
battery altogether insufficient to furnish the necessary quantity. 
Law of conduction of a discharge of common electricity through 
a straight conducting wire. ; 
24. If it be true, as we have supposed above, that the prin- 
cipal part of the resistance encountered by a discharge of com- 
mon electricity through a wire, is due to the induction of the cur- 
rent pon itself, it is obvious that the law of conductibility of — 
wires of different lengths for such discharges, is quite independ- 
ent of their conductibilities for galyanic currents. In proceeding — : 
to deduce the law of conductibility or conducting power for elec- 
tric discharges, so far as it has reference only to the induction of 
the current upon itself, it will be necessary to begin with a pre- 
cise definition of conducting power. In galvanic electricity the 
