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

WALKER'S PARATONNERRE. 583
by means of the rod u u', the plate z, and the binding
screw T.
WALKER'S PARATONNERRE.
In writing upon the subject of atmospheric electricity in
relation to its interference with the operation of the electric
telegraph, Mr. Charles V. Walker, one of the most distinguished
telegraph electricians in England, says:
" It is a well-known property of ordinary charges of electricity
to expand, so to speak, and to occupy the outside surface of
conducting bodies. If an ice-pail or metal vessel be insulated
on glass legs, and a brass ball hanging to a silk thread, be
employed to carry a charge of electricity from a common
electrical machine to the inside of the vessel, it will part with
all its charge the moment the two metals touch; and, on now
applying a test instrument to the inside of the ice-pail, no
electricity can be found there; the charge appears to have
vanished. But, on presenting it to the outside, the charge is
discovered there in its full quantity. I thence considered that,
whatever arrangement I should insert in the course of the conducting wire, I might very advantageously place this arrangement inside a stout metal cylinder, in good communication
with the earth; so that the charge, in that part of its course
should be in all but contact with the earth connection, and
further facilitated in its escape by having the latter on its
outside.
Fig. 19 represents the lightning conductor very nearly in
full size. A is a brass cylinder, one sixteenth of an inch thick (shown in section Fix. 10
in the figure), in perfect metallic communication with the earth by the stout wire. t
E, and insulated from the conducting wire
by a disk of boxwood a, and a boxwoodl
bobbin b b. The arrows show the diree-
tion of the charge from the line wire c to
the telegraph, to which it is screwed byl |
the end d. The ends of the bobbin closely |
fit the inner surface of the cylinder; but X |
it is slightly grooved in its course to re- 11 -
ceive two or three layers of a silk covered ^
copper wire g, finer than any elsewhere g K
to be found in the instrument; the wire |
is in the circuit, commencing at the thick | \
brass wire e, and terminating below at d,
and is in very close proximity to the earth,