[Transcriber's note: If the inductance is in henries and the capacitance
in farads, frequency in hertz = 1/(2 * PI * squareRoot( L * C ) )]
Vibration, Sympathetic.
A vibration in a cord or other body susceptible of elastic vibration
produced by the vibrations of exactly the same period in a neighboring
vibrating body. Thus if two tuning forks are tuned to precisely the same
pitch, and are placed near each other, if one is sounded it will start
the other into vibration by sympathy.
In electricity its application is found in electric resonance
experiments. The resonator has a definite period of electric resonance,
and is made to give a spark by the exciter of identical period. This is
by what may be called electric sympathetic vibration, and is exactly
analogous to the action of the tuning forks upon each other.
Vibrator, Electro-magnetic.
The make and break mechanism used on induction coils, or other similar
apparatus in which by alternate attractions by and releases from an
electro-magnet an arm or spring is kept in motion. In most cases the
work is done by a single magnet, whose armature is attracted to the
magnet, when the latter is excited, but against the action of a spring
which tends to pull it away from the magnet. In its motions a make and
break action is produced, to give the requisite alternations of
attraction and release. Two electro-magnets may be connected so as
alternately to be excited and keep an arm carrying a mutual armature in
vibration, or the same result may be attained by a polarized relay. The
make and break is illustrated under Bell, Electric--Coil, Induction--
Anvil.
Villari's Critical Value.
Magnetization induced or residual in a wire is diminished on stretching,
provided that the magnetization corresponds to an inducing force above a
certain critical value, known as above; this being (Sir Wm. Thomson)
about 24 times the terrestrial intensity. Below that critical value
tension increases the magnetization of a magnetized wire. The effects of
transverse expansive stress are opposed to those of longitudinal
stretching. (Daniell.)
Viole's Standard of Illuminating Power.
A standard authorized by the International Congress of 1881. It is the
light given by one square centimeter of platinum, melted, but just at
the point of solidification. It is equal to 20 English standard candles
almost exactly.
It has not been very widely accepted, the tendency among photometrists
being to adhere to the old standards, carcel or candle. It is obvious
that actual use of the Viole would be very inconvenient and would
involve expensive apparatus, difficult to work with.
Synonym--Viole.