Hughes' Electro-magnet.
A horseshoe electro-magnet with polarized core. It is made by mounting
two bobbins of insulated wire on the ends of a permanent horseshoe
magnet. It was devised for use in Hughes' printing telegraph, where very
quick action is required. The contact lasts only .053 second, 185
letters being transmitted per minute.
Fig. 197 HUGHES' ELECTRO-MAGNET.
Fig. 198. HUGHES' INDUCTION BALANCE.
Hughes' Induction Balance.
An apparatus for determining the presence of a concealed mass of metal.
The apparatus is variously connected. The cut shows a representative
form; a and a' are two primary coils, each consisting of 100 meters (328
feet) of No. 32 silk covered copper wire (0.009 inch diameter) wound on
a boxwood spool ten inches in depth; b and b' are secondary coils. All
coils are supposed to be alike. The primary coils are joined in series
with a battery of three or four Daniell cells. A microphone m is
included in the same circuit. The secondary coils are joined in series
with a telephone and in opposition with each other. The clock is used to
produce a sound affecting the microphone. If all is exactly balanced
there will be no sound produced in the telephone. This balance is
brought about by slightly varying the distance of one of the secondaries
from the primary, until there is no sound in the telephone. If now a
piece of metal is placed within either of the coils, it disturbs the
balance and the telephone sounds.