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

MAGNETOMETERS. 125
of this instrument is precisely the same as the one above
Fig. 14. S
t D
Fig. 15. described. It is nearer the simple multiplier devised by Schweigger.
<TA\ y.Fig. 16 represents the compass form
electrometer. The coil of wire is made to
~\| IIsurround an ordinary pocket compass, and
the strength of the electric current is
measured by the deflection of the needle.
The circle is divided into divisions as minute as may be required for the purposes
of its use. It is a very convenient instrument, and will be useful in the practice of
telegraphing.
Fig. 17 represents the most delicate form
of electrometer. It is capable of being
influenced by the slightest presence of electricity. On the base are placed two coils
of wire, as represented by fig. 10, between which is suspended
a delicate magnetic needle, with its mate or index needle
above a dial plate. The needle is suspended by a cocoon
thread from the top. Over the whole is placed a glass cover.
If there is any electricity in the coils, the index needle will
exhibit it and the quantity.
MA GNETOMETERS.
Various contrivances have been made to measure the magnetic force of electro-magnets. Fig. 18 is one gotten up by