For measuring a base line (in calculating a parallax) metal bars
or rods are used. These are carefully compared in the laboratory
with the standards and their lengths at a definite temperature
determined. Unfortunately, when these rods are taken into the
field for actual use they are exposed to constantly varying
temperatures, and they expand and contract in a very troublesome
way. Various devices have been used to eliminate the errors thus
introduced, the simplest and best being the Woodward “ice-bar
apparatus” used by the Coast and Geodetic Survey. In this the
metal measuring-bar is supported in a trough and completely
packed in ice, and thus maintained at the uniform temperature
of 32 degrees Fahr. With such an apparatus a base line can
be measured with an error of only a fortieth of an inch in a
mile, or one part in two and a half million.--CHARLES LANE
POOR, “The Solar System.”
(3053)
See EXCELLENCE IS COMPARATIVE.
=Standing by the Ship=--See LOYALTY.
=Stars and Stripes, Disrespect to the=--See PATRIOTISM,
LACK OF.
=Stars Converting a Skeptic=--See CONVERTED BY THE COMET.
=Stars, Gate of the=--See GATE, THE, OF STARS.
=State, The, More Than the Individual=--See REPRESENTATIVE DIGNITY.