6 A letter to Prof. Faraday. ‘ 
leave the element of perfection at one extremity, we involve the | 
element of perfection at the opposite.” Might it not be said of : 
light and darkness, or of opaqueness and translucency; in which | 
ease to resort to your language again, it might be added “espe 
cially as we have not in nature, a case of perfection at one ex-— | 
APeremity or the other.” But if there be not in nature, any two - 4 
bodies of which one possesses the property of perfectly resisting — 4 
the passage of electricity, while the other is endowed with the — 
faculty of permitting its passage without any resistance ; does this _ 
affect the propriety of considering the qualities of insulation and 
conduction in the abstract, as perfectly distinct, and inferring that _ 
so far as matter may be endowed with the one property, it must — 
be wanting in the other? 
Have you ever known electricity to pass through a pane of 4 
sound glass? My knowledge and experience create an impres- — 
sion that a coated pane is never discharged through the glass ul- y 
less it be cracked or perforated. That the property by which 
glass resists the passage of electricity, can be confounded with — 
_ that which enables a metallic wire to permit of its transfer, agree- 
ably to Wheatstone’s experiments, with a velocity greater than 
that of the solar rays, is to my mind inconceivable. : 
. You infer that the residual charge of a battery arises from the 
partial penetration of the glass by the opposite excitements. But — 
if glass be penetrable by electricity, why does it not pass throug | 
- it without a fracture or perforation ? a 
According to your doctrine, induction consists “in a forced state 
of polarization in contiguous rows of the particles of the glass” 
(1300); and since this is propagated from one side to the other, 
it must of course exist equally at all depths. Yet the 
penetration suggested. by you, supposes a collateral affection ‘ 
the same kind, extending only toa limited depth. Is this © 
sistent? Is it not more reasonable to suppose that the air in t 
vicinity of the coating gradually relinquishes to it a portion 
free electricity, conveyed into it by what you call ‘“ convection 
The coating being equally in contact with the air and gl 
appears to me more easy to conceive that the air might be 
trated by the excitement, than the glass. 
In paragraph 1300, I observe the following statement: “ 
a Leyden Jar is charged, the particles of the glass are 
EN io oso mereress condition —— clecti 
Siu 
hake 
