Double Fluid Theory.
A theory of electricity. Electricity is conveniently treated as a fluid
or fluids. According to the double fluid hypothesis negative electricity
is due to a preponderance of negative fluid and vice versa. Like fluid
repels like, and unlike attracts unlike; either fluid is attracted by
matter; the presence in a body of one or the other induces
electrification; united in equal proportions they neutralize each other,
and friction, chemical decomposition and other causes effect their
separation. The hypothesis, while convenient, is overshadowed by the
certainty that electricity is not really a fluid at all. (See Single
Fluid Theory--Fluid, Electric.)
Synonym--Symmer's Theory.
[Transcriber's note: Current is the motion of negative electrons in a
conductor or plasma. Unequal distribution of electrons is static
electricity. The relatively immobile nuclei of atoms are positive when
one or more of its electrons is absent and accounts for part of the
current in electrolysis and plasmas.]
Double Fluid Voltaic Cell.
A cell in which two fluids are used, one generally as depolarizer
surrounding the negative plate, the other as excitant surrounding the
positive plate. A porous diaphragm or difference in specific gravities
is used to keep the solutions separate and yet permit the essential
electrolytic diffusion. Grove's Cell, Bunsen's Cell, and Daniell's Cell,
all of which may be referred to, are of this type, as are many others.
Double Wedge.
A plug for use with a spring-jack. It has connection strips at its end
and another pair a little distance back therefrom, so that it can make
two loop connections at once.
Synonym--Double Plug.
Doubler.
A continuously acting electrophorous, q.v.; an early predecessor of the
modern electric machines. It is now no longer used.
D. P.
Abbreviation for Potential Difference.
Drag.
The pull exercised by a magnetic field upon a conductor moving through
it or upon the motion of an armature in it.
Dreh-strom. (German)
Rotatory currents; a system of currents alternating in periodic
succession of phases and producing a rotatory field. (See Field,
Rotatory--Multiphase Currents.)
Drill Electric.
A drill for metals or rock worked by an electro-magnetic motor. For
metals a rotary motion, for rocks a reciprocating or percussion action
is imparted. It is used by shipbuilders for drilling holes in plates
which are in place in ships, as its flexible conductors enable it to be
placed anywhere. For rock-drilling a solenoid type of construction is
adopted, producing rapid percussion.