94 Prof. Faraday on Electric Induction. 
Coulomb pointed out the difference of long and short as to the 
insulating or conducting power of such filaments, and like differ- 
ence occurs with long and short metal wires. 
he character of the phenomena described in this report indu- 
ces me to refer to the terms intensity and quantity as applied to 
electricity, terms which I have had so frequent occasion to em- 
ploy. These terms, or equivalents for them, cannot be dispensed 
with by those who study both the static and the dynamic rela- 
tions of electricity ; every current where there is resistance has 
the static element and induction involved in it, whilst every case 
of insulation has more or less of the dynamic element and con- 
duction ; and we have seen that with the same voltaic source, the 
same current in the same length of the same wire gives a difler- 
ent result as the intensity is made to vary, with variations of the 
inductién around the wire. The idea of intensity, or the power 
of overcoming resistance, is as necessary to that of electricity, 
either static or current, as the idea of pressure is to steam ina 
boiler, or to air passing through apertures or tubes; and we must 
have language competent to express these conditions and these 
ideas. Furthermore, I have never found either of these terms 
lead to any mistakes regarding electrical action, or give rise 1 
any false view of the character of electricity or its unity. I can 
not find other terms of equally useful significance with these ; of 
any, which, conveying the same ideas, are not liable to such mis- 
use as these may be subject to. It would be affectation, there 
fore, in me to search about for other words ; and besides that, the 
present subject has shown me more than ever their great value 
and peculiar advantage in electrical language. 
Note.—The fuse referred to in page 86 is of the following n& 
ture :—Some copper wire was covered with sulphuretted gutta 
percha ; after some months it was found that a film of sulphuret 
of copper was formed between the metal and the envelope; a0 
further that when half the gutta percha was cut away in any. 
place, and then the copper wire removed for about a quarter of 
an inch, so as to remain connected only by the film of sulphuret 
adhering to the remaining gutta percha, an intensity battery could 
cause this sulphuret to enter into vivid ignition, and fire gunpoW- 
der with the utmost ease. The experiment was shown in the 
lecture-room, of firing gunpowder at the end of eight miles of 
single wire. Mr. Faraday reported that he had seen it fired 
through 100 miles of covered wire immersed in the canal by the 
_use of this fuse. 

