r bodies. The second is that of amber, copal, gumsack, silk
thread, paper, and a number of other substances. The characteristic of
these two electricities is that a body of the vitreous electricity,
for example, repels all such as are of the same electricity, and on the
contrary attracts all those of the resinous electricity; so that the
tube, made electrical, will repel glass, crystal, hair of animals,
etc., when rendered electric, and will attract silk thread, paper,
etc., though rendered electrical likewise. Amber, on the contrary, will
attract electric glass and other substances of the same class, and
will repel gum-sack, copal, silk thread, etc. Two silk ribbons rendered
electrical will repel each other; two woollen threads will do the like;
but a woollen thread and a silken thread will mutually attract each
other. This principle very naturally explains why the ends of threads
of silk or wool recede from each other, in the form of pencil or broom,
when they have acquired an electric quality. From this principle one
may with the same ease deduce the explanation of a great number of
other phenomena; and it is probable that this truth will lead us to the
further discovery of many other things.

"In order to know immediately to which of the two classes of electrics
belongs any body whatsoever, one need only render electric a silk
thread, which is known to be of the resinuous electricity, and see
whether that body, rendered electrical, attracts or repels it. If it
attracts it, it is certainly of the kind of electricity which I call
VITREOUS; if, on the contrary, it repels it, it is of the same kind of
electricity with the silk--that is, of the RESINOUS. I have likewise
observed that communicated electricity retains the same properties; for
if a ball of ivory or wood be set on a glass stand, and this ball be
rendered electric by the tube, it will repel such substances as the
tube repels; but if it be rendered electric by applying a cylinder
of gum-sack near it, it will produce quite contrary effects--namely,
precisely the same as gum-sack would produce. In order to succeed in
these experiments, it is requisite that the two bodies which are
put near each other, to find out the nature of their electricity, be
rendered as electrical as possible, for if one of them was not at all or
but weakly electrical, it would be attracted by the other, though it be
of that sort that should naturally be repelled by it. But the experiment