The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

74 STATIC ELECTRICITY.
a single jar will retain, several are combined to form an
electrical battery. For convenience, the jars are placed in a
box with divisions, the bottom being lined with tin-foil, to
make connection with all the exterior coatings. The knobs of
the jars are connected together by wires, as represented in
fig. 16; and there is a metal hook projecting from the side of
the box connected with the tin-foil lining. Thus all the interior
Fig. 17.
and all the outside coatings of the jars are connected; and
when communication is made between the prime conductor
and any of the knobs of the jars, the whole are simultaneously
charged. They are also discharged simultaneously by making
connection between the projecting hook and any one of the
knobs.
The combination of several small jars is found better than
having a smaller number of large ones, because the thickness
of the glass necessary in jars of large size obstructs induction
through it. By an arrangement of many jars, an amount of
electric force may be accumulated that would almost equal the
destructive power of lightning. The battery used by Faraday
in his experiments consisted of fifteen equal jars, coated eight
inches upward from the bottom, and twenty-three inches in
circumference; so that each contained one hundred and eightyfour square inches of glass coated on both sides, independently
of the bottoms of the jars, which were of thicker glass, and
contained each about fifty square inches. The total coated
surface of the battery consequently comprised three thousand
five hundred square inches of coated surface. The electrical
battery at the Polytechnic Institution exposes a coated surface
of nearly eighty square feet. To receive the full charge of
such a battery would be instant death. A battery of nine