purpose he tried coins, pieces of metal, and
even a tea-kettle, "both empty and filled with hot or cold water"; but
he found that the attractive power appeared to be the same regardless of
the substance used.

"I next proceeded," he continues, "to try at what greater distances
the electric virtues might be carried, and having by me a hollow
walking-cane, which I suppose was part of a fishing-rod, two feet seven
inches long, I cut the great end of it to fit into the bore of the tube,
into which it went about five inches; then when the cane was put into
the end of the tube, and this excited, the cane drew the leaf-brass to
the height of more than two inches, as did also the ivory ball, when
by a cork and stick it had been fixed to the end of the cane.... With
several pieces of Spanish cane and fir-sticks I afterwards made a rod,
which, together with the tube, was somewhat more than eighteen feet
long, which was the greatest length I could conveniently use in my
chamber, and found the attraction very nearly, if not altogether, as
strong as when the ball was placed on the shorter rods."

This experiment exhausted the capacity of his small room, but on going
to the country a little later he was able to continue his experiments.
"To a pole of eighteen feet there was tied a line of thirty-four feet in
length, so that the pole and line together were fifty-two feet. With the
pole and tube I stood in the balcony, the assistant below in the court,
where he held the board with the leaf-brass on it. Then the tube being
excited, as usual, the electric virtue passed from the tube up the pole
and down the line to the ivory ball, which attracted the leaf-brass, and
as the ball passed over it in its vibrations the leaf-brass would follow
it till it was carried off the board."

Gray next attempted to send the electricity over a line suspended
horizontally. To do this he suspended the pack-thread by pieces of
string looped over nails driven into beams for that purpose. But when
thus suspended he found that the ivory ball no longer excited the
leaf-brass, and he guessed correctly that the explanation of this lay
in the fact that "when the electric virtue came to the loop that was
suspended on the beam it went up the same to the beam," none of it
reaching the ball. As we shall see from what follows, however, Gray had
not as yet determined that certain substances will conduct electricity
while others will not. But by a lucky accident he ma