the zenith and S. S. E. E. point of the horizon; between Ophiuchus and the meridian is Scorpio. Aquila and Antinous, E. S. E. Lyra, Vulpecula et Anser, Delphinus, and Equuleus, due east. The head of Draco, Cygnus, and Pegasus, are between the zenith and E. N. E. Andromeda, N. E. Cassiopeia, N. N. E. N.E. Ursa Major, the Lynx, Castor and Pollux, N.W., the latter near the horizon. Centaurus, Corvus, Crater, and Sextans in the horizon from the south to the west. Boötes between Virgo and the Zenith, the latter extending over a large portion of the sky in the S. W.

Telescopic Objects.

The following telescopic objects will be in favorable positions for observation during the month.

Hercules. In the girdle of Hercules, between two stars of the eighth magnitude, is a nebula round and bright in its centre; between the knee and left leg is another beautiful nebula 5' in diameter, surrounded with great nebulosity; near κ is another bright nebula, -each of these is resolvable into stars. In the breast of Hercules is a planetary nebula; a, the star in the head, is a double star-the large star red, the small of a bluish green color; this is also a variable star; period of variation 60 days. 8 is a double star, the largest of which is white, the small reddish white. y, k, p, n, and 70 are also double stars. The most interesting obwhich is a binary system,

ject in this constellation is 2, the large star of a beautiful bluish white, and the small of a fine ash color:-these stars revolve about their centre of gravity. On the 18th of July, 1782, the interval between the two stars was one half the diameter

of the smaller one, with a telescopic power of 460. In 1802 Sir William Herschel could no longer perceive the small star; but in a clear night in September of that year, with the same telescopic power as that before used, the apparent disc seemed to be a little lengthened in one direction. With the ten-feet telescope, and a power of 600, it had the appearance of a lengthened, or rather wedge-formed, star; this celebrated astronomer was convinced that not more than three-eighths of the apparent diameter of the small star was wanting to a complete occultation.

O Majestic Night!

Nature's great ancestor! Day's elder born!
And fated to survive the transient sun!
By mortals and immortals seen with awe!
A starry crown thy raven brow adorns,

An azure zone thy waist; clouds in heaven's loom
Wrought through varieties of shape and shade,
In ample folds of drapery divine,

Thy flowing mantle form, and, heaven throughout,
Voluminously pour thy pompous train.

COMETARY ASTRONOMY.

Magnitudes of Comets. The apparent magnitudes of comets not only depend on their absolute bulk, but also on their distances from the earth; some have appeared whose brightness did not exceed that of very minute stars, others have shone forth as stars of the first magnitude. That which appeared in the reign of Nero is described as not inferior in apparent magnitude to the sun. Hevelius observed a comet in 1652, which he describes as not less than the moon, though it was

deficient in splendour, having a pale dim light, and a dismal aspect. The comet of 1577 had an apparent diameter of 25' or 26', a magnitude nearly equal to that of the moon when in apogee. The diameter of the head of the comet of 1769 was about a degree, and its nucleus about 4'; that of 1807 had its envelope 6' in diameter, and the one that appeared in 1811 exceeded that of 1807 in apparent magnitude.

From the apparent angles under which comets are seen, being ascertained, and their distances determined, their true magnitudes are obtained. The

The second comet of 1811 possessed a nucleus of prodigious size, being no less than 2637 miles in diameter, or one-third of that of the earth. These diameters are the results of very careful measurements in the hands of good observers; which, however, very often vary, as determined by astronomers, who have measured the same body:-thus in the comet of 1811, Herschel computed the diameter to be the amount just stated, namely, 2637 miles; Schroëter, a celebrated astronomer, differed very widely from this result, and estimated the diameter to be only 570 miles. The great magnitude assigned to some comets, may be accounted for from the coma surrounding the nucleus, being measured instead of the nucleus; this would make a wonderful difference in the results. In this respect, also, comets differ from planets,-the edge of a planetary disc is

sharply defined, so that a micrometer may almost unerringly determine the angle it subtends; on the contrary, a cometary disc, from the nebulous matter through which it is seen, is generally rough and indistinct. Radiation, also, will cause the nucleus of a comet to appear larger than it really is, which is evident from the fact, that stars seen through the nebulous matter appear larger, though not brighter than when escaped from the vapoury medium. The comet of Halley was calculated to be about the magnitude of the moon, that of 1680 was supposed to be ten times as large as the moon; those comets which present merely a mass of nebulosity without a nucleus, vary in their sizes from that of 1804, which was 5000 miles in diameter, to that of the Encke comet, which, on its last return in 1828, was found to be 76000 miles in diameter; but it must be remembered, that these last mentioned contain very little matter in proportion to their magnitudes, being probably of not much greater density than the tails of some comets : this may be inferred from their pellucid nature,-the smallest stars being distinctly visible through every part of them.

The envelope that surrounds the nucleus, varies in depth considerably, and appears but in few instances to unite with the nucleus: the depth of the envelope of the comet of 1811 amounted, when at its maximum, to no less than 25,000 miles, and its distance from the centre of the nucleus 30,000 miles; the depth of the envelope of the comet of 1799 was estimated at nearly the same quantity.

The apparent lengths of the tails of comets vary from the smallest possible dimensions to that of the comet of

1618 and 1680, the former of which was more than a 100° in length; it must, however, be observed, that the tail of a comet will, at the same time, at different places, appear of different lengths, according to the states of the atmosphere at the different places of observation: there will also be a difference in the eyes of spectators at the same place; hence the disagreement between the estimates of astronomers: -at the time that the tail of the comet of 1680 was said to be 90°, as observed at London, it was stated to be 120° at Constantinople. It may be concluded that when the tail of a comet appears of considerable length, that it is then not very remote from the earth.

Comets may appear to be destitute of tails from their positions, relative to the earth and sun; if a comet approaches the sun in the direction of the earth, the axis of the tail is then coincident with the line of vision, consequently it appears with only a coma surrounding the nucleus without any divergency, and in every case where the line of vision does not pass, so as to form a right angle with the axis of the tail, it must appear shorter than it really is.

As the apparent lengths of these streams of light are in some instances very great, so are also their true lengths-that of the comet of 1744 was calculated to be 20 millions of miles in extent, and that of 1769, a tail of 40 millions; the tail of the great comet of 1680 was computed to be no less than 100 millions of miles, and the second comet of 1811 had a vast projecting luminosity extending 132 millions of miles,-a length so vast as almost to overpower the faculties with astonishment,--for supposing the nucleus of this comet to be