ariner, appeared; it
comprised the usual matter of annual almanacs, and was enriched with
such precepts and rules in the practice of navigation and traffic as are
in daily use. But in 1767 our nautical almanac, a tabular statement of
the geocentric planetary positions, which may be said to have created a
new era in voyaging, was published; and this book, with certain
alterations, was in force up to 1830, when a commission of the Royal
Society and astronomers established the present _Ephemeris_, now so much
valued. It is published annually, but computed to four years in advance,
to accommodate those proceeding on long voyages. Attempts have been made
in other countries to publish _The Nautical Almanac_, improved and
corrected, but they are mere copies, corrected by the errata furnished
annually in advance.

EPICYCLOID. A geometrical curve generated by making a circle roll upon
the circumference of another circle; it is found useful in determining
the figure of the teeth of wheel-work, and other purposes in mechanics.
If the generating circle proceeds along the convexity of the periphery,
it is called an upper or exterior epicycloid; if along the concavity, a
lower or interior epicycloid.

EPOCH. The time to which certain given numbers or quantities apply.

EPROUVETTE. A small piece of ordnance specially fitted for testing the
projectile force of samples of gunpowder.

EQUATED ANOMALY. This is also called the true anomaly, and is the
distance of the sun from the apogee, or a planet from its aphelion, seen
from the sun.

EQUATION, ANNUAL. _See_ ANNUAL EQUATION.

EQUATION OF EQUINOXES. The difference between the mean and apparent
places of the equinox.

EQUATION OF THE CENTRE. The difference between the true and mean
anomalies of a planet.

EQUATION OF TIME. The difference between mean and apparent time, or the
acceleration or retardation of the sun's return to the meridian.

EQUATOR. Called also the equinoctial line, or simply the line, being an
imaginary circle round the earth, dividing the globe into two equal
parts, and equally distant from both poles. Extended to the heavens, it
forms a circle called the celestial equator, which in like manner
divides the heavens into two equal parts, the northern and southern
hemispheres.

EQUATORIAL CURRENT. The set, chiefly westerly, so frequently met with
near the equator, especially in the Atlantic Oceans.

EQUATORIAL DOLDRUMS. _See_ DOLDRUMS.

EQUATORIAL SECTOR. A