calculating them, we must refer to our volume for 1819: as this variation is much slower than that which takes place with respect to the phase of Venus, we shall insert the result of the calculation only every third month.

Mercury will obtain his greatest elongation on the 13th of this month. Mars will be in opposition at half past 10 in the evening of the 16th. Venus and Jupiter will be in conjunction at 27 m. after 11 in the evening of the 18th, at which time Venus will be 47" south of Jupiter. The Moon will be in conjunction with Mars at 20 m. after 7 in the morning of the 2d. With the star marked a, in Virgo, at 1 m. after midnight of the 8th. With a, in Scorpio, at 23 m. after 11 in the morning of the 12th. With Saturn at 7 m. after 8 in the evening of the 19th. And with ẞ, in Taurus, at 2 m. after 4 in the morning of the 25th. The Moon will also be in perigee on the 16th, and in apogee on the 30th.

EXPLANATIONS in PRACTICAL ASTRONOMY.

Having in the former volumes of Time's Telescope given a familiar explanation of many of the leading principles in the science of astronomy, we shall now avail ourselves of this renewed opportunity to add a few brief explanations, examples, and illustrations of the practical part of that science; and as White's Ephemeris is one of the most useful and practical compendiums, as well as one which is familiar to all who study this part of the subject, we shall principally confine our observations to the terms and tables inserted in that work; referring, however, to some of the other almanacs, whenever such a reference has a tendency to render our remarks more useful.

The Sun's Declination

Is his distance either northward or southward from the equinoctial line, which is measured on a celestial meridian passing through his centre. Declination, therefore, corresponds with latitude, or distance from the equator, in geography. This declination is readily found for any given time by computation; for, knowing the Sun's place in the ecliptic, the general rule is,

As radius

Is to the sine of the Sun's longitude,

So is the sine of the obliquity of the ecliptic
To the declination required.

Astronomers, therefore, compute this declination for every day at apparent noon, or the moment when the centre of the Sun passes the first meridian of the country for which the computation is made: in England, this is done for the Royal Observatory, at Greenwich. The declination thus found, is then formed into tables for practical use; that is, to be employed in such other astronomical calculations as require it as one of their elements. One of the first and most frequent uses which the young astronomer is required to make of this declination, is that of finding the altitude of the Sun from having the latitude of the place of observation given. This is at once so easy and obvious an operation, that a simple illustration will be sufficient; for since the height of the equator is always equal to the co-latitude of the place of observation, when the latitude is known, the height of the equator is also given; and consequently, if the declination of the Sun be added to this height, or subtracted from it, as circumstances may require, and the refraction also be taken into the account, the apparent meridian altitude of the Sun's centre will be obtained. This is the first thing to be done in making observations with a transit instrument; for then the instrument may be placed at its

proper elevation, so that the centre of the wires may correspond with the apparent centre of the Sun.

As an example of this computation, let the apparent meridian altitude of the Sun's centre be required, at the Royal Observatory, Greenwich, on the 30th of May, 1820. The latitude of the observatory being 51° 28′ 40′′, the complement of this is 38° 31′20′′, which is the height of the equator; and the declination on the 20th of May being north, the Sun will necessarily be above that circle, and consequently the declination must be added to its height; hence

Now, as the refraction always renders the apparent altitude of any of the heavenly bodies greater than the true altitude, this quantity, which for the above altitude is about 35", being added to the above sum, gives 58° 33′ 30′′ for the apparent altitude of the Sun's centre at the time required.

If the declination had been south, it must have been subtracted from the co-latitude, and the difference would have been 18° 29′ 45′′; to which the refraction being added, would give 18° 32′ 37′′ for the apparent altitude of the Sun's centre, in that

case.

If the place at which the observation is to be made be not upon the meridian for which declination is calculated, and it be thought necessary to correct it for this difference of longitude, this may be done by a simple proportion; for as 24 hours is to the time between the Sun's passing the meridians of the two places, so is the difference between the declinations answering to the two days to the correction required; which must be added to declination in the table, or subtracted from it, according as it is increasing or decreasing.

The Sun's declination is also used in a variety of

other astronomical calculations, which may be briefly enumerated here, and some of which will be illustrated in the subsequent pages. From what is explained above, it is obvious that it is necessary in finding the latitude of a place from an observation of the meridian altitude of the Sun; and it is also equally requisite in finding the latitude from two observed altitudes with the interval of time between them. It is likewise used in computing the Sun's azimuth from his altitude and the latitude of the place, in order to find the variation of the mariner's compass; as well as in computing the Sun's altitude from the latitude of the place and the horary angle. The Sun's declination is also necessary to be used in calculating the apparent time from an observed altitude of the Sun at a distance from the meridian, the latitude of the place of observation being known; or to compute the time of the Sun's rising and setting. For any of these purposes, the declination taken from the table should be reduced to that corresponding to the required time, by the preceding proportion.

The Naturalist's Diary

For JANUARY 1820.

Soft floated the clouds in the fields of blue ether;
The earth with fresh flowers was still covered o'er;
Like Egypt's enchantress, whom age could not wither,
They bloomed, though the season of youth was no more.
The voice of delight was long heard from the thorn,
Its tenants no end to their happiness knew;

The evening of love was as sweet as its morn,

And the bird of the spring lingered all the year thro'.

And even that day, whose return we revere,
Though often it lours in our northern skies,
Arose with mild aspect, unclouded, and clear,
As of old it appeared to the Bethlemites' eyes.

SUCH is the poetical description of the winter of 1818-19, as it was experienced in England. The singularly mild temperature of this winter, and the

want of frost and snow, was not confined to our own island; it was equally observed in almost all parts of the European Continent. In Sweden, and most parts of Russia, they had, instead of the usual degree of cold, a temperature of several degrees above the freezing point. This was the case even in Lapland, to the north of Tornea, where, instead of the usual cold of 20% of Reaumur, they had 6° of warmth. This want of frost and snow proved a serious inconvenience in these northern regions, by preventing the conveyance of the iron ore from the mines in Sweden to the smelting houses; and in Russia, the carriage of goods from the interior to the seaports for exportation, which is regularly done in the winter, when the hard frozen ground, covered with snow many feet deep, affords a solid, even, and commodious road.

From the Meteorological Journal kept at the Botanic Garden of Geneva, the same phenomenon, of want of snow, appears to have occurred on the Alps. In the three months of October, November, and December, there was only once so much as a white frost. In the whole course of November, says the Journal, the snow has not lain a single day on the mountains that surround our lake. This is a phenomenon of which the oldest inhabitants can remember no previous instance. The wheat is remarkably beautiful; the cattle are still in pasture as in the month of September.' The same Journal, for December, says, the continued fineness of the temperature, during this month, is without parallel in our country. Mount Jura, which is generally covered with snow in November, is still almost totally free from it to-day, the 31st of December. There is none at all on the summit of La Dole, and very little on the summits near fort L'Ecluse. In consequence of the dryness of the temperature all the year, the springs are very low, and we begin to be uneasy for next year, seeing that the mountains have no snow at all on them.'