Anti-magnetic Shield.
In general terms a hollow screen of soft iron designed to protect any
mass of steel behind or enclosed by it from magnetization by any magnet
near it, such as a dynamo field magnet. This it does by concentrating
the lines of force within its own mass, so that the space within it or
enclosed by it is comparatively free from lines of force. It is often
applied to watches, and is virtually an iron case in which they are
enclosed.
Antimony.
A metal, one of the elements, atomic weight, 122:
equivalent, 40.6 and 24.4; valency, 3 and 5;
specific gravity, 6.8.
It is a conductor of electricity.
Relative resistance, compressed (silver = 1), 23.60
Specific resistance, 35.50 microhms.
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 3.418 ohms.
(b) 1 foot long, 1/1000 inch thick, 213.6 "
(c) 1 meter long, weighing 1 gram, 2.384 "
(d) 1 meter long. 1 millimeter thick, 0.4521 "
Resistance of a 1-inch cube, 13.98 microhms.
Approximate percentage resistance per degree C.
(1.8º F. at 20º C. 88º F.) 0.389 per cent.
Elcctro-chemical equivalent (hydrogen = .0105) .2560
(See Thermo-Electric Series.)
Anvil.
An intermittent contact, or "make and break" of the current is sometimes
produced by directly pressing a key down upon a metallic surface, the
two being terminals of the circuit. The surface or stud on which such
pressure is produced is called the anvil. The ordinary telegraph key,
which makes a contact by the pressure of the operator's fingers does it
by making a contact between a contact piece upon the front end of the
key and the anvil. In the induction coil the anvil is also found. Thus
in the cut representing the end of an induction coil and its circuit
breaker in which O and O' and P and P' represent the secondary circuit
terminal connections A is the core of soft iron wires, h is the anvil;
the hammer when resting upon it so as to be in contact closes the
circuit. When the current coming from the primary to the post i, passes
through the hammer and anvil h, and emerges by m, it magnetizes the
core; this attracts the hammer, which is made of or is armed with a mass
of iron. This breaks the circuit. The hammer falls at once on the anvil,
again making the circuit, and the action is repeated with great
rapidity. Hammer and anvil or key and anvil connections should be made
of platinum.
Fig. 17. INDUCTION COIL CIRCUIT BREAKER.