22. MERCURY, the nearest Planet to the Sun, goes round him (as in the
circle marked ☿) in 87 days 23 hours of our time nearly; which is the
length of his year. But, being seldom seen, and no spots appearing on
his surface or disc, the time of his rotation on his axis, or the length
of his days and nights, is as yet unknown. His distance from the Sun is
computed to be 32 millions of miles, and his diameter 2600. In his
course, round the Sun, he moves at the rate of 95 thousand miles every
hour. His light and heat from the Sun are almost seven times as great as
ours; and the Sun appears to him almost seven times as large as to us.
The great heat on this Planet is no argument against it’s being
inhabited; since the Almighty could as easily suit the bodies and
constitutions of it’s inhabitants to the heat of their dwelling, as he
has done ours to the temperature of our Earth. And it is very probable
that the people there have such an opinion of us, as we have of the
inhabitants of Jupiter and Saturn; namely, that we must be intolerably
cold, and have very little light at so great a distance from the Sun.
[Sidenote: Has like phases with the Moon.]
23. This Planet appears to us with all the various phases of the Moon,
when viewed at different times by a good telescope; save only that he
never appears quite Full, because his enlightened side is never turned
directly towards us but when he is so near the Sun as to be lost to our
sight in it’s beams. And, as his enlightened side is always toward the
Sun, it is plain that he shines not by any light of his own; for if he
did, he would constantly appear round. That he moves about the Sun in an
Orbit within the Earth’s Orbit is also plain (as will be more largely
shewn by and by, § 141, _& seq._) because he is never seen opposite to
the Sun, nor above 56 times the Sun’s breadth from his center.
[Sidenote: His Orbit and Nodes.]
24. His Orbit is inclined seven degrees to the Ecliptic; and _that_ Node
§ 20, from which he ascends northward above the Ecliptic is in the 14th
degree of Taurus; the opposite, in the 14th degree of Scorpio. The Earth
is in these points on the 5th of _November_ and 4th of _May_, new style;
and when Mercury comes to either of his Nodes at his[5] inferior
Conjunction about these times, he will appear to pass over the disc or
face of the Sun, like a dark round spot. But in all other parts of his
Orbit his Conjunctions are invisible, because he either goes above or
below the Sun.
[Sidenote: When he will be seen as if upon the Sun.]
25. Mr. WHISTON has given us an account of several periods at which
Mercury may be seen on the Sun’s disc, _viz._ In the year 1782, _Nov._
12th, at 3 h. 44 m. in the afternoon: 1786, _May_ 4th, at 6 h. 57 m. in
the forenoon: 1789, _Dec._ 6th, at 3 h. 55 m. in the afternoon; and
1799, _May_ 7th, at 2 h. 34 m. in the afternoon. There will be several
intermediate Transits, but none of them visible at _London_.
[Sidenote: Fig. I.