58

Dr. Young's Refractions, the Barometer being at 30 inches, and the inter nal Thermometer at 50, or the external at 47, degrees; with the corrections one inch in the barometer, and for one degree in the thermom

for

eter of Fahrenheit. From page 19 of Vol. 1st of Pearson's Practical As

The correction for an increase of altitude of one inch in the barometer, or for a depression of one degree in the thermometer, is to be added to the tabular refraction; but when the barometer is lower than 30 inches, or the thermometer higher than 50 degrees, the correction becomes subtractive. When great accuracy is required, 0,003 inch should be deducted from the observed height of the barometer, for each degree that the thermometer near it, is above 50 degrees, and the same quantity added, for an equal depression.

Mean Solar into Sidereal Time + 0.0011874

A second of time, at the Equator, contains 1521 feet.

Elements of the Eclipse of the Sun on Sunday, November 30th, Mean Time at Greenwich.

H. M.

Sun's Horizontal Parallax 8.70''. Obliquity of the Ecliptic 23° 27' 40.4''.

Lunar Elements, computed for every half hour.

Longitude. Latitude. Right Asc.

Declination.

Equat. Par. Semi. Diam.

Elements of the Eclipses of January 9th, June 7th, June 21st, and December 15th, Mean Time at Greenwich.

The sign+prefixed to the hourly motion of the Moon in latitude indicates that she is approaching, and the sign that she is receding from, the north pole of the ecliptic. The hourly increase of the Sidereal time is constantly 9,8565 seconds.

II. METEOROLOGICAL INFORMATION.

[From the Companion to the British Almanac for 1833.]

I. ON COMETS.

THE year which has just passed away has been distinguished by the predicted appearance* of two comets, the most remarkable which have yet fallen under the notice of astronomers. These are what are commonly called the comets of Encket and Biela ‡. The latter has been an object of fear to many on account of the nearness with which it has approached, not the earth, but a point of the earth's path. As public attention has thus been turned to this subject in an unusual degree, we seize this opportunity of laying before our readers a slight account of the present state of cometary astronomy, distinguishing that which we really know of these bodies from the many surmises to which they have given rise.

The signification of the word comet has varied, as new bodies have appeared which analogy has led astronomers to include under that name. It was first given, as the word denotes, to bodies which appeared in the heavens with a train of light, or tail, and thus included some of the meteors which belong to our own atmosphere. We now apply the word to those heavenly bodies, without the limits of our own atmosphere, which are nebulous in their appearance, and with or without a tail. We may divide all which have been observed into three classes : 1. Those whose returns have been predicted, and the prediction verified by the fact. These are three in number, viz. the celebrated comet

* Mr. Henderson has observed Encke's comet at the Cape of Good Hope, and Sir John Herschel that of Biela. We mention these facts here, as neither body is visible to the naked eye, and many of our readers may not be aware of their having been seen by

any one.

↑ First discovered by M. Pons, November 26, 1818, but justly named by astronomers after Professor Encke, from his success in detecting its orbit, motion, and perturbations. First discovered by M. Biela, an Austrian officer, February 28th, 1826.