Radiometer.
An instrument consisting of four vanes poised on an axis so as to be
free to rotate, and contained in a sealed glass vessel almost perfectly
exhausted. The vanes of mica are blackened on one side.
On exposure to light or a source of heat (ether waves) the vanes rotate.
The rotation is due to the beating back and forth of air molecules from
the surface of the vanes to the inner surface of the glass globe.
Radiometer, Electric.
A radiometer in which the motion of the molecules of air necessary for
rotation of the vane is produced by electrification and not by heating.
Radio-micrometer.
An instrument for detecting radiant energy of heat or light form. It
consists of a minute thermopile with its terminals connected by a wire,
the whole suspended between the poles of a magnet. A minute quantity of
heat produces a current in the thermopile circuit, which, reacted on by
the field, produces a deflection. A convex mirror reflecting light is
attached so as to move with the thermopile. The instrument is of
extraordinary sensitiveness. It responds to .5E-6 of a degree Centigrade
or about 1E-6 degree Fahrenheit.
Radiophony.
The production of sound by intermittent action of a beam of light upon a
body. With possibly a few exceptions all matter may produce sound by
radiophouy.
Range Finder.
An apparatus for use on shipboard to determine the distance of another
ship or object. It is designed for ships of war, to give the range of
fire, so as to set the guns at the proper elevation. The general
principle involved is the use of the length of the ship if possible, if
not of its width, as a base line. Two telescopes are trained upon the
object and kept trained continuously thereon. The following describes
the Fiske range finder.
The range finder comprises two fairly powerful telescopes, each mounted
on a standard, which can be rotated round a vertical axis, corresponding
with the center of the large disc shown in the engraving. One-half of
the edge of this disc is graduated to 900 on either side of a zero
point, and below the graduation is fixed a length of platinum silver
wire. This wire only extends to a distance of 81.10 on either side of
zero, and is intended to form two arms of a Wheatstone bridge. The
sliding contact is carried by the same arm as the telescope standards,
so that it moves with the telescope. The two instruments are mounted at
a known distance apart on the ship, as shown diagrammatically in the
cut. Here A and B are the centers of the two discs, C and D the arms
carrying the telescopes, and E and F the platinum silver wires. Suppose
the object is at T, such that A B T is a right angle, then
AT=AB/sin(ATB).