Valency.
The relative power of replacing hydrogen or combining therewith
possessed by different elements; the number of atomic bonds belonging to
any element. Thus oxygen has a twofold valency, is bivalent or is a
dyad, and combines with two atoms of hydrogen because the latter has a
unitary atomicity, is monovalent or is a monad.
Valve, Electrically Controlled.
A valve which is moved by or whose movements are regulated by
electricity.
In the block system of railroad signaling the semaphores are worked by
weights and pneumatic cylinders and pistons. The valves for admitting or
releasing the compressed air are operated by coil and plunger mechanism.
There are many other instances of the control of valves by the electric
current.
Vapor Globe.
A protecting glass globe surrounding an incandescent lamp, when the lamp
is to be used in an atmosphere of explosive vapor, as in mines or
similar places; or when in a place where it is exposed to dripping water
which would break the hot lamp bulb if it fell upon it.
Variable Period.
The period of adjustment when a current is started through a conductor
of some capacity. It is the period of duration of the variable state, q.
v., in a conductor. As indicated in the next definition in a cable of
high electrostatic capacity a variable period of nearly two minutes may
exist. This indicates the retardation in signaling to be anticipated in
cables and other lines of high capacity.
Variable State.
When an electric circuit is closed the current starts through the
conductor with its full strength from the point of closure, and advances
with a species of wave front so that some time elapses before it attains
its full strength in the most distant parts of the conductor, owing to
its having to charge the conductor to its full capacity at the given
potential. The state of the line while the current thus varies is called
the variable state.
A long telegraph line when a message is being transmitted may be always
in the variable state. The current at the receiving end may never attain
its full strength.
In the case of such a conductor as the Atlantic cable, 108 seconds would
be required for a current to attain 9/10 of its full strength at the
distant end, and but 1/5 second to attain 1/100 of its final value.
During the period of increase of current the variable state exists.
Variation of the Compass.
The declination of the magnetic needle. (See Elements, Magnetic.) As the
declination is subject to daily, annual and secular variations, it is
unfortunate that this term is synonymous with declination. Thus the
variation of the compass means its declination, while there is also the
variation of the declination and of other elements. The term variation
of the compass is more colloquial than the more definite expression
"declination," or "magnetic declination."