Actinic Rays.
The rays of light at the violet end of the spectrum; also the invisible
rays beyond such end, or the ether waves of short periods which most
strongly induce chemical change.
Actinism.
The power possessed by ether waves of inducing chemical change, either
of decomposition or of combination. The violet and ultra-violet end of
the spectrum of white light, generally speaking, represent the most
highly actinic rays.
Actinometer, Electric.
Properly an apparatus for measuring the intensity of light by its action
upon the resistance of selenium. A current produced by fixed
electro-motive force passing through the selenium affects a galvanometer
more or less according to the intensity of the light. It is more
properly an electric photometer. The term has also been applied to a
combination of a thermo-electric pile and galvanometer, the light
falling on the pile affecting the motions of the galvanometer.
Action, Local.
(a) The wasteful oxydation of the zinc in a galvanic battery due to
local impurities and variations in the composition of the zinc. These
act to constitute local galvanic couples which cause the zinc to
dissolve or oxydize, without any useful result. Amalgamation of the zinc
prevents local action. Chemically pure zinc is also exempt from local
action, and can be used in an acid battery without amalgamation. (See
Amalgamation.)
(b) The same term has been employed to indicate the eddy or foucault
currents in dynamo electric machines. (Sec Current, Foucault.)
Activity.
The rate of doing work; the work done per second by any expenditure of
energy. The activity of a horse-power is 550 foot lbs. per second, or
746 volt-coulombs per second. The practical electric unit is the
volt-ampere, often called the watt. (Sec Energy, Electric.)
Adapter.
A screw coupling to engage with a different sized screw on each end; one
of the uses is to connect incandescent lamps to gas-fixtures.
A. D. C.
Abbreviation for Anodic Duration Contraction, q. v.; a term in
electro-therapeutics.
Adherence, Electro-magnetic.
The adherence between surfaces of iron due to elcctro-magnetic
attraction. It has been applied to the driving-wheels of an engine and
rail, whose grip is increased by such action. In one method a deep
groove was cut around the wheel which was wound with a magnetizing coil.
Thus one rim becomes a north and the other a south pole, and the rail
completing the circuit acts as the armature. Such an arrangement
prevents a wheel from sliding. Electro-magnetic adherence has also been
employed to drive friction gear wheels. In one arrangement the two
wheels are surrounded by a magnetizing coil, under whose induction each
attracts the other, developing high adherence between their peripheries.