Circle of Right Ascension to Clock

Great circles passing through the poles of the equinoctial.

Declination Circles. The great circles upon which declinations are measured.

Diurnal Circle. A heavenly body is said to describe a diurnal circle owing to the apparent daily revolution of the celestial sphere.

Hour Circle. The great circle of the celestial sphere passing through the poles of the heavens and perpendicular to the equinoctial.

Latitude Circles. Great circles perpendicular to the plane of the ecliptic, upon which latitudes are measured.

Polar Circle. The small circles of the terrestrial sphere parallel to the equator.

They are 23 deg. 28 min. from the poles; the northern is termed the Arctic circle, and the southern the Antarctic circle.

Vertical Circle. A great circle passing through the zenith.

An altitude of a heavenly body when it is near the meridian--either A. M. or P. M.

To sail round.

To circumnavigate the globe is to sail entirely around the world.

Near the pole.

Commonly known as "mackerel" sky and "sheep in a meadow" sky, owing to the rounded woolly patches.

Long layers of cloud, thinner at the edges than in the centre.

The highest and least dense of cloud formation; it is of many varieties in relation to shape and extent.

(See Civil Time.)

The civil day commences at midnight and comprises 24 hours, which are divided into two equal parts--the first 12 (from midnight to noon) being named A. M., and the last 12 (noon to midnight) named P. M.

The screw on the back of the sliding limb of an instrument of reflection by which the limb is rendered immovable when desired.

An instrument for showing the roll of a vessel when suspended in a thwartships line. When it is suspended in a fore-and-aft line it will record the pitch of the vessel.

A machine composed of a combination of wheels, which are moved either by weights or by a spring, and which measures time, indicating the same by hour, minute, and second hands moving around the dial, or face of the instrument, on which numerals are painted.

Astronomical Clock. A pendulum clock of superior workmanship and great accuracy. It shows sidereal (star) time, and when the first point of Aries is on the meridian it indicates oh. om. os.

Mean Solar Clock. A timepiece which shows mean solar or civil time.

Sidereal Clock. An astronomical clock.