FOR JULY, 1827.
(For the Mirror.)
The sun is in apogee, or at his greatest distance from the earth on the 2nd, in 10 deg. Cancer; he enters Leo on the 23rd, at 5h. 13m. afternoon; he is in conjunction with the planet Saturn on the 2nd at 11h. 30m. morning, in 9 deg. Cancer, and with Mars on the 12th at 1h. 45m. afternoon, being advanced 10 deg. further in the eliptic.
Venus and Saturn are also in conjunction on the 26th at 3h. afternoon, in 13 deg. Cancer.
Mercury will again be visible for a short time about the middle of the month a little after the sun has set, arriving on the 16th at his greatest eastern elongation, or apparent distance from the centre of the system, as seen from the earth in 20 deg. Leo; and in aphelio, or that point of his orbit most distant from the sun, on the 22nd; he becomes stationary on the 29th.
There is only one visible eclipse of Jupiter's first satellite this month—on the 5th, at 10h. 21m. evening.
The Georgium Sidus, or Herschel, comes to an opposition with the sun on the 19th, at 6h. 15m. evening; he is then nearest the earth, and consequently in the most favourable position for observation; he began retrograding on the 1st of May in 28 deg. 12m. of Capricornus; he rises on the 1st, at 9h. 11m. evening, culminating at 1h. 16m., and setting at 5h. 21m. morning, pursuing the course of the sun on the 17th of January; he moves only 13m. of a deg. in the course of the month, rising 2h. earlier on the 31st.
This planet, called also Uranus, was discovered by Herschel on the 13th of March, 1781. It is the most distant orb in our system yet known. From certain inequalities on the motion of Jupiter and Saturn, the existence of a planet of considerable size beyond the orbit of either had been before suspected; its apparent magnitude, as seen from the earth, is about 3-1/2 sec., or of the size of a star of the sixth magnitude, and as from its distance from the sun, it shines but with a pale light, it cannot often be distinguished with the naked eye. Its diameter is about 4-1/2 times that of the earth, and completes its revolution in something less than 83-1/2 years. The want of light in this planet, on account of its great distance from the sun, is supplied by six moons, which revolve round their primary in different periods. There is a remarkable peculiarity attached to their orbits, which are nearly perpendicular to the plane of the ecliptic, and they revolve in them in a direction contrary to the order of the signs.
"Moore," in an old almanack, speaking on the difference of light and heat enjoyed by the inhabitants of Saturn, and the earth, says,—
"From hence how large, how strong the sun's bright ball,
But seen from thence, how languid and how small,
When the keen north with all its fury blows,
Congeals the floods and forms the fleecy snows:
'Tis heat intense, to what can there be known,
Warmer our poles than in its burning (!) zone;
One moment's cold like their's would pierce the bone,
Freeze the heart's blood, and turn us all to stone."
Were Saturn thus situated, what would the inhabitants of Herschel feel, whose distance is still further?—pursuing this train of reasoning, the heat in the planet Mercury would be seven times greater than on our globe, and were the earth in the same position, all the water on its surface would boil, and soon be turned into vapour, but as the degree of sensible heat in any planet does not depend altogether on its nearness to the sun, the temperature of these planets may be as mild as that of the most genial climate of our globe.
The theory of the sun being a body of fire having been long since exploded, and heat being found to be generated by the union of the sun's rays with the atmosphere of the earth, so the caloric contained in the atmosphere on the surfaces of the planets may be distributed in different quantities, according to the situation they occupy with regard to the sun, and which is put into action by the influence of the solar rays, so as to produce that degree of sensible heat requisite for each respective planet. We have only to suppose that a small quantity of caloric exists in Mercury, and a greater quantity in Herschel, which is fifty times farther from the sun than the other, and there is no reason to believe that those planets nearest the sun suffer under the action of excessive heat, or that the more distant are exposed to the rigours of insufferable cold, which, in either case, might render them unfit for the abodes of intellectual beings.
PASCHE.