Appendix I, Continued
TEMPERATURE.Intensity or degree of
heat. Fahrenheit temperature is based upon
a scale in which water freezes at 32° and
boils at 212°.
TERRESTRIAL SPHERE.The Earth.
THERMOMETER.An instrument for
instrument consisting essentially of a circle
graduated in degrees to which is attached
one fixed arm and two arms pivoted at the
center and provided with clamps so they
can be set at any angle to the fixed arm
within the limits of the instrument.
TIDE.The periodic rise and fall of the
surface of oceans, bays, and so forth, due
principally to the gravitational attraction of
the Moon and Sun for the rotating Earth.
TIME DIAGRAM.A diagram in which
the celestial equator appears as a circle and
celestial meridians and hour circles as
radial lines, used to facilitate solution of
time problems and others involving arcs of
the celestial equator or angles at the pole
by indicating relations between various
TRACK.To follow the movements of an
object, as by radar or an optical system.
TRANSMITTER.One who or that which
transmits or sends anything, particularly a
TROPICAL CYCLONE.A violent
cyclone originating in the tropics.
TWILIGHT.The periods of incomplete
darkness following sunset (evening
twilight) or preceding sunrise (morning
UNION JACK.Flag flown at the bow of
a ship moored or anchored, consisting of
the union of the national flag. Also flown
in the boat of a high official and at a
yardarm during a general court-martial or
court of inquiry.
UPPER BRANCH.That half of a
meridian or celestial meridian from pole to
pole that passes through a place or its
VARIATION.The angle between the
magnetic and geographical meridians at
any place, expressed in degrees east or
west to indicate the direction of magnetic
north from true north.
VECTOR.A straight line representing
both direction and magnitude.
VECTOR DIAGRAM.A diagram of
more than one vector drawn to the same
scale and reference direction and in correct
position relative to each other.
VERNAL EQUINOX.That point of
intersection of the elliptical and the
celestial equator occupied by the Sun as it
changes from south to north declination on
or about March 21.
VISIBILITY.The extreme horizontal
distance at which prominent objects can be
seen and identified by the unaided eye.