Declination of the Magnetic Needle.
The deviation of the magnetic needle from the plane of the earth's
meridian. It is also called the variation of the compass. (See Magnetic
Elements.)
Decomposition.
The reduction of a compound substance into its constituents, as in
chemical analysis. The constituents may themselves be compounds or
proximate constituents, or may be elemental or ultimate constituents.
Decomposition, Electrolytic.
The decomposition or separation of a compound liquid into its
constituents by electrolysis. The liquid must be an electrolyte, q. v.,
and the decomposition proceeds subject to the laws of electrolysis, q.
v. See also Electrolytic Analysis.
Decrement.
When a suspension needle which has been disturbed is oscillating the
swings gradually decrease in amplitude if there is any damping, as there
always is. The decrement is the ratio of the amplitude of one
oscillation to the succeeding one. This ratio is the same for any
successive swings.
De-energize.
To cut off its supply of electric energy from an electric motor, or any
device absorbing and worked by electric energy.
Deflagration.
The explosive or violent volatilizing and dissipating of a substance by
heat, violent oxidation and similar means. It may be applied among other
things to the destroying of a conductor by an intense current, or the
volatilization of any material by the electric arc.
Deflecting Field.
The field produced in a galvanometer by the current which is being
tested, and which field deflects the needle, such deflection being the
measure of the current strength.
Deflection.
In magnetism the movement out of the plane of the magnetic meridian of a
magnetic needle, due to disturbance by or attraction towards a mass of
iron or another magnet.
Deflection Method.
The method of electrical measurements in which the deflection of the
index of the measuring instrument is used as the measure of the current
or other element under examination. It is the opposite of and is to be
distinguished from the zero or null method, q. v. In the latter
conditions are established which make the index point to zero and from
the conditions necessary for this the measurement is deduced. The
Wheatstone Bridge, q. v., illustrates a zero method, the sine or the
tangent compass, illustrates a deflection method. The use of deflection
methods involves calibration, q. v., and the commercial measuring
instruments, such as ammeters and volt meters, which are frequently
calibrated galvanometers, are also examples of deflection instruments.