persons emit sparks in pulling off their flannels or silk
stockings. The fur of a cat, or even of a garment, stroked in the
dark with a warm dry hand will be seen to glow, and perhaps heard
to crackle. During winter a person can electrify himself by
shuffling in his slippers over the carpet, and light the gas with
a spark from his finger. Glass and sealing-wax are, however, the
most convenient means for investigating the electricity of
friction.

A glass rod when rubbed with a silk handkerchief becomes, as we
have seen, highly electric, and will attract a pithball (fig. 2).
Moreover, if we substitute the handkerchief for the rod it will
also attract the ball (fig. 3). Clearly, then, the handkerchief
which rubbed the rod as well as the rod itself is electrified. At
first we might suppose that the handkerchief had merely rubbed off
some of the electricity from the rod, but a little investigation
will soon show that is not the case. If we allow the pithball to
touch the glass rod it will steal some of the electricity on the
rod, and we shall now find the ball REPELLED by the rod, as
illustrated in figure 4. Then, if we withdraw the rod and bring
forward the handkerchief, we shall find the ball ATTRACTED by it.
Evidently, therefore, the electricity of the handkerchief is of a
different kind from that of the rod.

Again, if we allow the ball to touch the handkerchief and rub off
some of its electricity, the ball will be REPELLED by the
handkerchief and ATTRACTED by the rod. Thus we arrive at the
conclusion that whereas the glass rod is charged with one kind of
electricity, the handkerchief which rubbed it is charged with
another kind, and, judging by their contrary effects on the