VALUE OF THE PRINCIPAL AND OTHER ARTICLES OF FOREIGN AND COLONIAL PRODUCE AND MANUFACTURES

Tons.

No.

Tons.

British.

381,083

83,048,629

1

DEFINITION OF ASTRONOMICAL TERMS. Aberration. An apparent change of place in the fixed stars, which arises from the motion of the earth combined with the motion of light. Altitudes.-The Altitude of an object is that portion of a vertical circle which is intercepted between the centre of the celestial object and the horizon.

Aphelion. That point in the orbit of a planet in which it is at its greatest distance from the sun.

Apogee. That point in the orbit of the moon or a planet in which it is at its greatest distance from the earth.

Azimuths.-The Azimuth of an object is its true bearing, east or west, of its nearest meridian. It is always equal to that portion of the horizon which is intercepted between the vertical circle passing through the centre of the object and the meridian of the place of observation.

Declination of a Celestial Object.—The Declination of any celestial object is its distance north or south from the equinoctial, and is measured by that portion of the celestial meridian which is intercepted between the centre of the object and the equinoctial.

Disk of the Sun or Moon is its round face, which, on account of the great distance of the object, appears flat as like a plane surface.

Diurnal -Diurnal motions of the planets are the spaces they move through in a day.

Elongation. The angular distance of a planet from the sun as it appears to us upon the earth.

Emersion. The time when any planet which is eclipsed begins to recover its light again.

The Horizon.-The visible horizon is that which is seen while the eye is elevated above the surface; and the sensible is that which is seen when the eye is on a level with the water. The depression of the former below the latter is called the dip of the visible horizon.

Immersion. The moment when an eclipse begins, or when a planet enters into a dark shadow.

Libration. An apparent irregularity of the moon's motion, which makes her appear to librate about her axis in such a manner that parts of her eastern and western limbs become visible and invisible alternately.

Parallax.-Parallax is the difference between an altitude taken at the surface of the earth, and that taken at the centre at the same time. When the object is on the horizon, it is called the horizontal parallax ; but in any other case it is called the parallax in altitude.

Penumbra.-A faint shadow which accompanies an eclipse and occasions a partial obscurity of the body to that part of the earth on which it falls.

Perigee. That point of the moon or a planet's orbit in which it is at its least distance from the earth.

Perihelion. That point of a planet's orbit in which it is at its least distance from the sun.

Phases.-The several appearances of the moon and planets, according as a greater or less part of their illuminated hemispheres are presented to our sight.

Prime Vertical Circle.-The Prime Vertical Circle is the circle which passes from the zenith due east or west, having 90 degrees of the horizon intercepted between it and the meridian. All objects on this circle are said to be on the prime vertical.

Polar Distance of any celestial object, is an arc of a meridian, contained between the centre of that object and the pole of the equinoctial; or, in other words, it is the distance of the object from the elevated pole.

Refraction.-Refraction is a quantity by which a body appears above its true place in the heavens.

Right Ascension.-The Right Ascension of a celestial body is that portion of the equinoctial which is intercepted by a celestial meridian passing through the centre of the body and the first point of the ecliptic. It is generally given in time.

Right Ascension of the Meridian.-The Right Ascenson of the Meridian is that part of the equinoctial that comes to the Meridian with the object measured from the first point of Aries.

Terrestrial and Celestial Equators.—The Terrestrial Equator is a great circle (supposed to be described) around the earth, at an equal distance, or 90 degrees from the poles, dividing the globe into two equal parts; the part to the southward of the equator being called the southern hemisphere, and that to the northward the northern hemisphere.

The Celestial Equator, commonly called the Equinoctial, is an imaginary circle described in the heavens, corresponding to and coinciding with the terrestrial equator.

Time.-Time is measured by the apparent motion of a celestial body over the surface of the globe, and is called Solar, Lunar, or Sidereal, according to the body with which it is referred; a full revolution of either of these objects is called its apparent day, and begins when the object comes to the meridian; but for the convenience of civil and commercial business, that of the sun, called solar or civil time, is from midnight to midnight, the first twelve hours of which are marked A. M., signifying ante meridian, and the last twelve hours P. M., signifying post meridian. In this and the following mode of keeping time, the day is dated as soon as it commences.

Astronomical Day.-This day is also measured by the apparent motion of the sun, but for the convenience of astronomical computations, it is taken to begin at noon, that is, 12 hours after the beginning of the civil day, and end at noon of the following day. Astronomers generally reckon the hours of this day up to 24 hours, without any distinction of ante or post meridian, which they call astronomical time; hence the first 12 hours of which are the P. M. hours of the civil day on which it begins, and the last 12 hours of it are the A. M. hours of the day on which it ends.

The Nautical Day.-This day, as well as the civil and astronomical day, is measured by the apparent motion of the sun. It begins just with the astronomical day, but it is dated with the noon on which it ends; hence it is 24 hours in date later than the astronomical day, the first 12 hours of which are marked in the journal with P. M., and the last 12 hours with A. M., so that occurrences which happen on the afternoon of the civil day on which it begins, come in the journal under the date of the civil day in which it ends. The Log Book is generally kept in nautical or Sea Time, but it may be kept in Common or Civil Time.

Tropics.-The Tropics are two circles (supposed to be described) parallel to the equator, at the distance of about 23° 28′, equal to the highest declination. The northernmost is called the Tropic of Cancer, and the other the Tropic of Capricorn.