Diagometer.
An apparatus for use in chemical analysis for testing the purity of
substances by the time required for a charged surface to be discharged
through them to earth. It is the invention of Rousseau.
An electrometer is charged with a dry pile. One of its terminals is
connected with one surface of the solution or substance to be tested,
and the other with the other surface. The time of discharge gives the
index of the purity of the substance.
Diamagnetic Polarity.
Treating diamagnetism as due to a polar force, the polarity of a
diamagnetic body is the reverse of the polarity of iron or other
paramagnetic bodies. A bar-shaped diamagnetic body in a field of force
tends to place itself at right angles to the lines of force.
Diamagnetism.
(a) The science or study of diamagnetic substances and phenomena.
(b) The magnetic property of a diamagnetic substance.
Diameter of Commutation.
The points on the commutator of a closed circuit ring--or
drum--armature, which the brushes touch, and whence they take the
current, mark the extremities of the diameter of commutation. Were it
not for the lag this would be the diameter at right angles to the line
connecting the centers of the opposite faces of the field. It is always
a little to one side of this position, being displaced in the direction
of rotation. In open circuit armatures the brushes are placed on the
diameter at right angles to this one, and sometimes the term diameter of
commutation is applied to it. All that has been said is on the
supposition that the armature divisions correspond not only in
connection but in position with those of the armature coils. Of course,
the commutator could be twisted so as to bring the diameter of
commutation into any position desired.
Diapason, Electric.
A tuning-fork or diapason kept in vibration by electricity. In general
principle the ends of the fork act as armatures for an electro-magnet,
and in their motion by a mercury cup or other form of contact they make
and break the circuit as they vibrate. Thus the magnet alternately
attracts and releases the leg, in exact harmony with its natural period
of vibration.
Diaphragm.
(a) In telephones and microphones a disc of iron thrown into motion by
sound waves or by electric impulses, according to whether it acts as the
diaphragm of a transmitter or receiver. It is generally a plate of
japanned iron such as used in making ferrotype photographs. (See
Telephone and Microphone.)
(b) A porous diaphragm is often used in electric decomposition cells and
in batteries. The porous cup represents the latter use.
[Transcriber's note: Japanned--covered with heavy black lacquer, like
enamel paint.]