Torsion Head.
The handle and disc from whose undersurface the filament depends to
which the needle or magnet is attached. It is turned to measure the
torsional effect, the edge of the disc being marked or graduated so as
to give the angle of deflection required to overcome the effect of the
torque of the needle.
Torsion Suspension.
Suspension by one or more wires, fibres, or ribands, involving the
restitutive force of torsion. Thus fibre suspension, q. v., is a variety
of torsion suspension.
Often a single riband of steel stretched horizontally and secured at
both ends is used, the suspended object, e. g., a balance beam, being
attached at its own centre to the centre of the stretched riband. Quite
sensitive balances are constructed on this principle. It is peculiarly
available where an electric current is to be transmitted, as absolute
contact is secured, as in William Thomson's ampere balances.
Touch.
A term applied to methods of magnetization, as "single touch," "double
touch," or "separate touch," indicating how the poles of the inducing
magnet or magnets are applied to the bar to be magnetized. Under the
titles of Magnetization the different methods are described.
Tourmaline.
A mineral; a subsilicate; characterized by the presence of boric
trioxide, which replaces aluminum oxide. It is notable for possessing
pyro-electric properties. (See Pyro-electricity.)
Tower, Electric.
The tower used in the tower system, q. v., of arc light illumination.
Tower System.
In electric lighting the system of lighting extended areas by powerful
arc lamps placed on high towers, generally of iron or steel frame-work.
The lights are thus maintained at a high elevation, giving greater
uniformity of illumination than if they were lower, but at the expense
of considerable light which is lost. Sometimes wooden masts are employed
instead of towers.
The principle involved is that the intensity of light at any place given
by a source of illumination varies with the square of its distance from
the place in question. Hence in using strong arc lights it is an object
to have the distances of all parts of the area illuminated at as nearly
uniform distances from the light as possible. An approximation to
uniformity is secured by placing the lamps at a very high elevation.