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

126 ELECTRO-MAGNETISM.
Mr. Charles T. Chester, of New-York, as an attachment to the
electro-magnet used on the Morse telegraph. The ends of the
coils are seen below; the measurement scale is seen above.
The armature of the magnet is connected with the index
finger, and the slightest magnetic influence will be exhibited.
Fig. 19 represents Hearder's magnetometer. A B is a strong
base of wood, about four feet long and one foot wide, to which
are attached four levelling screws; D D are two strong iron
uprights, firmly screwed into the base and connected at the
top by a stout iron cross piece, E, having a hole in the centre,
through which passes the screw, F, of the strong double sus.
Fig. 16.
pension hook G. Two iron nuts, H H, serve to fix the suspension hook at any height. i i is a light and delicate, but strong
steel yard, being graduated on one side to correspond with the
distance between the knife-edge K and M; these are respectively one and two inches apart. Different weights may be
employed; on the arm N is a rest to support the long arm of
the lever, and it is capable of being adjusted to any height by
a tightening screw in the hollow socket o. The different parts
of the scale are marked by letters, each of which will be readily
understood by the reader. The magnet, u u, is wound with