Directive Power.
In magnetism the power of maintaining itself in the plane of the
magnetic meridian, possessed by the magnetic needle.
Discharge, Brush.
The static discharge of electricity into or through the air may be of
the brush or spark form. The brush indicates the escape of electricity
in continuous flow; the spark indicates discontinuity. The conditions
necessary to the production of one or the other refer to the nature of
the conductor, and of other conductors in its vicinity and to the
electro-motive force or potential difference; small alterations may
transform one into the other. The brush resembles a luminous core whose
apex touches the conductor. It is accompanied by a slight hissing noise.
Its luminosity is very feeble. The negative conductor gives a smaller
brush than that of the positive conductor and discharges it more
readily. When electricity issues from a conductor, remote from an
oppositely excited one, it gives an absolutely silent discharge, showing
at the point of escape a pale blue luminosity called electric glow, or
if it escapes from points it shows a star-like centre of light. It can
be seen in the dark by placing a point on the excited conductor of a
static-electric machine.
Synonyms--Silent Discharge--Glow Discharge.
Discharge, Conductive.
A discharge of a static charge by conduction through a conductor.
Discharge, Convective.
The discharge of static electricity from an excited conductor through
air or rarefied gas; it is also called the quiet or silent discharge.
The luminous effect in air or gas at atmospheric pressures takes the
form of a little brush from a small positive electrode; the negative
shows a star. The phenomena of Gassiot's cascade, the philosopher's egg
and Geissler tubes, all of which may be referred to, are instances of
convective discharge.
Discharge, Dead Beat.
A discharge that is not oscillatory in character.
Discharge, Disruptive.
A discharge of a static charge through a dielectric. It involves
mechanical perforation of the dielectric, and hence the mere mechanical
strength of the latter has much to do with preventing it. A disruptive
discharge is often oscillatory in character; this is always the case
with the discharge of a Leyden jar.