electric
atmospheres, which exist round metallic bodies, and which differ very
little in respect to the proportions of their vitreous and resinous
ingredients.

Thus also, though where the accumulated electricities are dense, as in
charging a coated glass-jar, the glass, which intervenes, may be of
considerable thickness, and may still become charged by the stronger
attraction of the secondary electric ethers; but where the spontaneous
adhesive electric atmospheres are employed to charge plates of air, as
in the Galvanic pile, or probably to charge thin animal membranes or
cuticles, as perhaps in the shock given by the torpedo or gymnotus, it
seems necessary that the intervening nonconducting plate must be
extremely thin, that it may become charged by the weaker attraction of
these small quantities or difference of the spontaneous electric
atmospheres; and in this circumstance only, I suppose, the shocks from
the Galvanic pile, and from the torpedo and gymnotus, differ from
those of the coated jar.

3. When atmospheres of electricity, which do not differ much in the
quantity or proportion of their vitreous and resinous ethers, approach
each other, they are not easily or rapidly united; but the predominant
vitreous or resinous ether of one of them repels the similar ether of
the opposed atmosphere, and attracts the contrary kind of ether.

The slowness or difficulty with, which atmospheres, which differ but
little in kind or in density, unite with each other, appears not only
from the experiment of Mr. Canton above related, but also from the
repeated smaller shocks, which may be taken from a charged coated jar
after the first or principal discharge, if the conducting medium has
not been quickly removed, as is also mentioned above.

Hence those atmospheres of either kind of electric matter, which
differ but very little from each other in kind or quantity, require
the most perfect conductors to cause them to unite. Thus it appears by
Mr. Bennet's doubler, as mentioned in the Preliminary Proposition, No.
VI. that the natural adhesive atmosphere round silver contains more
vitreous electricity than that naturally round zinc; but when thin
plates of these metals, each about an ounce in weight, are laid on
each other, or moderately pressed together, their atmospheres do not
unite. For metallic plates, which when laid on each other, do not
adhere, cannot be said to be in real contact, of which their not
adhering is a proof;