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the bubble to the middle without reversing the level, for then the axis upon which it rests will evidently be horizontal.
The telescope itself likewise requires some attention in its adjustment, or in making the foci of the eye and object-glasses coincide, and then bringing the wires to this common point. Some telescopes have the object-glass fixed, while the eye-glass and wires are moveable; and others have the wires fixed, and the two glasses moveable; a different mode of adjustment is consequently requisite for each. Iu the first case, the eye-piece must be slided in or out till the object appears perfectly distinct. Then the wires being also moved backwards or forwards till they also appear distinct, the telescope will be fit for use. The mode of adjustment in the second case, is by moving the eye-glass till the wires acquire their greatest clearness, and then changing the position of the object-glass till the object also assumes its maximum brightness, when the telescope will be perfectly adjusted. This adjustment is of great importance in making accurate observations, and the following is an easy method of trying its correctness. Bring the horizontal wire to bisect a star very correctly as it passes the meridian, and it will then appear to run along the wire. If the eye be moved a little upwards or downwards while the star is passing the field of view, and it does not appear to quit the wire, the reticule is correctly placed ; if it does leave the horizontal wire, the proper screw must be turned till it does not.
Another important adjustment is, that of bringing the instrument into the plane of the meridian. To accomplish this, take several altitudes of the Sun near the meridian, noting the respective times by a watch or clock; and from these find the apparent time, the latitude of the place and the Sun's declination being known. The difference between this time and the mean of those given by the clock or
the wirthe horizoes not. liustment the mer of the wa
watch will be what the watch is too slow or too fast, in reference to apparent time. When the watch is too fast, add the difference to 12 hours; but when it is too slow, subtract it from 12 hours, and the sum or remainder will be the time when the Sun's centre will pass the meridian, as nearly as the exactness of the watch can be depended upon. Then the Sun's semidiameter (taken from the Nautical Almanac for the given day) added to, and subtracted from, this time, will give the two moments when his eastern and western limbs will be on the meridian. A short time before the Sun's western limb will reach the meridian, let a person count the seconds, and name the minutes aloud by the clock as they pass; and while he is doing this, bring the Sun within the field of view of the instrument, by elevating it to the required altitude, and turning the whole instrument round on the proper screw, until the middle wire is west of the Sun's western limb. As the telescope inverts the image, it will then necessarily appear to be on the eastern side of the eastern limb. The screw then being tightened, when the Sun's nearest limb arrives at the wire, keep it on it by turning the instrument at the same rate as the Sun moves, till he who counts the seconds arrives at the instant when this limb of the Sun should pass the meridian"; and the instrument will then be nearly in its proper position. The counting of the seconds should still proceed till the moment when, according to the calculation, the eastern limb should be upon the meri. dian, which affords another opportunity of correcting the position of the instrument, if it does not exactly coincide with the central wire at the time calculated...
Having thus brought the instrument either into, or yery near, the meridian, its real situation may be verified by several methods. One of the most convenient, if the latitude be sufficient, is by means of circumpolar stars. When the latitude exceeds 25
quent and below the poles observed, it is ofransit
or 30 degrees, there are several stars which are sufficiently bright and never set, and which may consequently be observed when on the meridian both above and below the pole. The transit in both these positions being correctly observed, it is obvious that, if the time between the upper and lower transit be exactly equal to that between the lower and upper, the instrument will be exactly in the meridian; but if the former of these periods be greater than the latter, the telescope points to the east of the true meridian; but if the latter be the greater interval, it is west of it, and must be adjusted accordingly; for which a repetition of the observation may be necessary.
When its meridional position is thus correctly ascertained, place a mark as distant from the telescope as circumstances will permit, and adjust it, by this mark, previously to every observation.
but if the ope poinperiods be the meridi up
The Naturalist's Diary
For MAY 1823.
LUCRETIUS, by Good, L. ii, v. 14. How delightful is the opening of May, bringing with it the most delicious sensations, overflowing with sweets, and infusing through all nature a freshness and vitality perceived at no other period of the year! Summer may possess attractions of a more flaunting character, and Autumn may proffer its matured fruits and wealthy harvests; but to those who have a keen perception of natural beauty, and a sympathy with the vivid impressions which Spring produces on the mind, what can be more grateful than the renovated appearance of nature, and the elasticity and exhilaration of foeling experienced at the beginning of this month of fruition, pregnant as it is with light, pleasure, and loveliness? The clouds, no longer black, and hurried across the face of heaven by storms, are like fleeces of snowy whiteness enamelled upon the eternal azure, setting off and not sullying the purity of its serene hue. The soft breezes,
· Zephyr with Aurora playing, bear buxon health' and joyousness on their wings. The birds sing their sweetest notes.
The insect youth are on the wing,
And float amid the liquid noon. The early flowers, the yellow cowslip and the pale primrose,' decorate the surface of the earth. The verdure, rich in colour, refreshed by frequent showers, and not yet imbrowned by the summer sun, may be contemplated in all its variety of tinge. Creation seems to have arisen from the dead; all is being-instinct with life and motion. Love also awakes at this genial season, as Cunningham pleasingly sings:
From the west as it wantonly blows,
Fond Zephyr caresses the vine;
And willows and woodbines entwine :
That border the vernal alcove,
For May is the niother of Love.
The stock-dove, recluse with her mate,
Conceals her fond bliss in the grove,
“That May is the mother of Love.' To all conversant with the writings of the poets, striking descriptions of the seasons must be familiar. No piece by the hand of Guido or the Caracci exceeds the following group of allegorical personages, as drawn by that master poet LUCRETIUS:
SPRING comes and Venus, and with foot advanced,
MASON GOOD. Milton makes the most heavenly clime to consist of an eternal spring :
The birds their quire apply; airs, vèrnal airs,
Led on the eternal spring. Virgil, in his second Georgic, places the cosmogony in the spring :
Snch were the days, the season was the same,
WARTON, Geo. L. ii, v. 407. And again, the Mantuan bard, in his first Georgic, exquisitely describes the season of spring: this we shall give in the beautiful version of Mr. SOTHEBY:
Birds on their branches hymeneals sing,