51. Dr. LONG, in the first volume of his Astronomy, pag. 168, mentions
an ingenious and easy method of finding nearly what proportion the land
bears to the sea; which is, to take the papers of a large terrestrial
globe, and after separating the land from the sea with a pair of
scissars, to weigh them carefully in scales. This supposes the globe to
be exactly delineated, and the papers all of equal thickness. The Doctor
made the experiment on the papers of Mr. SENEX’s seventeen inch globe;
and found that the sea papers weighed 349 grains, and the land only 124:
by which it appears that almost three fourth parts of the surface of our
Earth between the Polar Circles are covered with water, and that little
more than one fourth is dry land. The Doctor omitted weighing all within
the Polar Circles; because there is no certain measurement of the land
there, so as to know what proportion it bears to the sea.
[Sidenote: The Moon.]
52. The MOON is not a Planet, but only a Satellite or Attendant of the
Earth, moving round the Earth from Change to Change in 29 days 12 hours
and 44 minutes; and going round the Sun with it every year. The Moon’s
diameter is 2180 miles; and her distance from the Earth 240 thousand.
She goes round her Orbit in 27 days 7 hours 43 minutes, moving about
2290 miles every hour; and turns round her Axis exactly in the time that
she goes round the Earth, which is the reason of her keeping always the
same side towards us, and that her day and night taken together is as
long as our lunar month.
[Sidenote: Her Phases.]
53. The Moon is an opaque Globe like the Earth, and shines only by
reflecting the light of the Sun: therefore whilst that half of her which
is toward the Sun is enlightened, the other half must be dark and
invisible. Hence, she disappears when she comes between us and the Sun;
because her dark side is then toward us. When she is gone a little way
forward, we see a little of her enlightened side; which still increases
to our view, as she advances forward, until she comes to be opposite to
the Sun; and then her whole enlightened side is towards the Earth, and
she appears with a round, illumined Orb; which we call the _Full Moon_:
her dark side being then turned away from the Earth. From the Full she
seems to decrease gradually as she goes through the other half of her
course; shewing us less and less of her enlightened side every day, till
her next change or conjunction with the Sun, and then she disappears as
before.
[Sidenote: A proof that she shines not by her own light.