hat certain
bodies are "electrics" and others "non-electrics"--that is, that some
substances when rubbed show certain peculiarities in attracting pieces
of paper and foil which others do not. Dufay proved that all bodies
possess this quality in a certain degree.

"I have found that all bodies (metallic, soft, or fluid ones excepted),"
he says, "may be made electric by first heating them more or less and
then rubbing them on any sort of cloth. So that all kinds of stones, as
well precious as common, all kinds of wood, and, in general, everything
that I have made trial of, became electric by beating and rubbing,
except such bodies as grow soft by beat, as the gums, which dissolve in
water, glue, and such like substances. 'Tis also to be remarked that the
hardest stones or marbles require more chafing or heating than others,
and that the same rule obtains with regard to the woods; so that box,
lignum vitae, and such others must be chafed almost to the degree of
browning, whereas fir, lime-tree, and cork require but a moderate heat.

"Having read in one of Mr. Gray's letters that water may be made
electrical by holding the excited glass tube near it (a dish of water
being fixed to a stand and that set on a plate of glass, or on the brim
of a drinking-glass, previously chafed, or otherwise warmed), I have
found, upon trial, that the same thing happened to all bodies without
exception, whether solid or fluid, and that for that purpose 'twas
sufficient to set them on a glass stand slightly warmed, or only
dried, and then by bringing the tube near them they immediately became
electrical. I made this experiment with ice, with a lighted wood-coal,
and with everything that came into my mind; and I constantly remarked
that such bodies of themselves as were least electrical had the greatest
degree of electricity communicated to them at the approval of the glass
tube."

His next important discovery was that colors had nothing to do with the
conduction of electricity. "Mr. Gray says, towards the end of one of
his letters," he writes, "that bodies attract more or less according to
their colors. This led me to make several very singular experiments.
I took nine silk ribbons of equal size, one white, one black, and the
other seven of the seven primitive colors, and having hung them all in
order in the same line, and then bringing the tube near them, the
black one was first attracted, the white one next, and others in order
successivel