Any method of obtaining measurements or comparisons, in which the measurement is correct when the deflection of the galvanometer or other indicator is zero, nought or null. The Wheatstone Bridge (see Bridge, Wheatstone) is an example of a null method. Two obvious advantages attach to null methods in electric galvanometer work. One is that an [...]

The pole of a magnet which tends to point to the north; the north pole of a magnet.

(a) The north-seeking pole of a magnet; the pole of a magnet which tends to point to the north, and whence lines of force are assumed to issue on their course to the other pole of the magnet. (b) The North Pole of the earth. Treating the earth as a magnet, and accepting the above [...]

A material that does not conduct electricity except with great difficulty; a substance of very high resistance. Synonym–Insulator–Dielectric.

A deposit obtained in electroplating, characterized by irregular thickness; due to too low density of current.

When a dilute solution of copper acetate is placed on a bright silver plate and a strip of zinc is touched to the silver beneath the copper, a series of rings of copper are formed by electrolysis around the zinc. These are Nobili’s rings. If for the copper acetate a solution of lead oxide in [...]

An alarm bell in a telegraph office, which bell is connected at night to give a loud signal to attract the operator’s attention. It is used in telephone exchanges and is connected so as to ring as long as a subscriber remains unanswered after calling.

A bath for the electro-deposition of nickel. A great many formulae have been given. Metallic nickel is dissolved in 1 vol. sulphuric acid mixed with 2 vols. water. Neutralize with ammonia, and add of ammonium sulphate one-half the weight of metallic nickel originally used; 135 parts of nickel will be enough for a bath of [...]

A metal; one of the elements; atomic weight, 58.8 ; equivalent, 29.4; valency, 2; specific gravity, 8.8. It is a conductor of electricity. Relative resistance, annealed (Silver = 1),   8.285 Specific Resistance,                         12.47   microhms. Resistance of a wire (a) 1 foot long, weighing 1 grain,      15.206   ohms. (b) 1 foot long, 1/1000 inch thick,     74.963    [...]

Symbol or contraction for “nominal horse power.” This is a basis for rating the size of an engine.