MACHINA ELECTRICA ET APPARATUS CHEMICUS.

MACHINA ELECTRICA, or the Electrical Machine, was introduced among the constellations by Bode. It is between the Phoenix and the Sea Monster. There is scarcely a star in the group visible to the naked eye.

The Chemical Apparatus, or Apparatus Chemicus, is also south of Cetus, and may be found in one of the bends of the River. It contains two stars of the third magnitude, the others are much smaller. We owe this group to La Caille.

Canis Major.-Sceptrum Brandenbergium.-Monoceros.-Lepus.-Columba.Argo Navis.-Officina Typographica.-Cola Sculptoris.-Horologium.— Plateum Pictoris.-Pyxis Nautica.*

CANIS MAJOR.-THE GREAT DOG.

Position, &c.-This constellation contains the largest and brightest star in the heavens. This star is in the head of the Dog, and is named Sirius. A line drawn through the three stars in the belt of Orion, towards the south, will point it out. Sirius is supposed to be nearer the earth than any of the other stars. J. Cassini has attempted to show that Sirius has an annual parallax of six seconds, and from this it would follow that its distance from our earth is nearly eighteen thousand times greater than that of the Sun; but from more accurate examinations, it appears that the parallax of this star is altogether insensible, and therefore that its distance cannot be estimated. About five degrees west of Sirius, we find Beta in the fore-paw of Canis Major; and a little to the east of that star may be observed Mu, Gamma, and Iota, in the head; Mu and Gamma form with Sirius a triangle somewhat in the shape of a dog's head. To the south of Sirius, there are four bright stars disposed in the outlines of the upper part of a pair of scales; of these Zeta is in the northern hindpaw, Delta is in the body, and Eta in the tail of the Dog. The star Gamma was invisible to Miraldi in 1670, and in 1692-3, appeared to the same astro

The head of the Hydra drawn on this Plate is noticed in our Description of the next Plate.

nomer of the fourth magnitude; but from later observations, no change in its apparent magnitude can be discovered.

Canis Major is bounded by Monoceros, Lepus, Columba, Argo Navis, and Officina Typographica.

The ancients imagined that the rising of the Dog Star with the Sun, occasioned the sultry weather and the diseases usually experienced in the latter part of summer, and hence they called this season the dog days. The Romans sacrificed a brown dog every year to appease the rage of Sirius. The rising of the stars, however, not only varies according to the latitude of different places, but is always later and later every year in the same place, so that in time Sirius may, by the same rule, be charged with bringing frost and snow when he rises in the winter. In our almanacs the season of dog days is set down as occurring from the third of July to the eleventh of August, without any regard to the position of Sirius. In England, the dog days have caused some variety in their calendar. Bede refers to a time when they commenced on the fourteenth of July; in the reign of Elizabeth they were reckoned from the sixth of that month to the sixth of September; from the restoration of Charles II. to the correction of the calendar, the beginning of this period was on the nineteenth of July, and the end of it, on the twenty-eighth of August; after the correction of the calendar the time was changed to the thirtieth of July and the seventh of September; and of late in the English almanacs they are placed as we first mentioned.

The rising and setting of brilliant stars was much attended to by ancient nations, because in this manner they ascertained the proper seasons for their various agricultural employments, and for the observance of their religious ceremonies. But by the aid of modern science, we can now calculate the precise position of the heavenly bodies at any required time, and we are thus relieved from a wearisome and anxious attention to the rising and setting of these stars.

History. The Greeks, as usual, have many fables to account for the origin