231. Let us suppose that there are two little balls moving equably round
a celestial Globe by clock-work, one always keeping in the Ecliptic, and
gilt with gold, to represent the real Sun; and the other keeping in the
Equator, and silvered, to represent the fictitious Sun: and that whilst
these balls move once, round the Globe according to the order of Signs,
the Clock turns the Globe 366 times round it’s Axis westward. The Stars
will make 366 diurnal revolutions from the brasen Meridian to it again;
and the two balls representing the real and fictitious Sun always going
farther eastward from any given Star, will come later than it to the
Meridian every following day; and each ball will make 365 revolutions to
the Meridian; coming equally to it at the beginnings of Aries, Cancer,
Libra, and Capricorn: but in every other point of the Ecliptic, the gilt
ball will come either sooner or later to the Meridian than the silvered
ball, like the patches above-mentioned. This would be a pretty-enough
way of shewing the reason why any given Star, which, on a certain day of
the year, comes to the Meridian with the Sun, passes over it so much
sooner every following day, as on that day twelvemonth to come to the
Meridian with the Sun again; and also to shew the reason why the real
Sun comes to the Meridian sometimes sooner, sometimes later, than it is
noon by the clock; and, on four days of the year, at the same time;
whilst the fictitious Sun always comes to the Meridian when it is twelve
at noon by the clock. This would be no difficult task for an artist to
perform; for the gold ball might be carried round the Ecliptic by a wire
from it’s north Pole, and the silver ball round the Equator by a wire
from it’s south Pole, with a few wheels to each; which might be easily
added to my improvement of the celestial Globe, described in N^o 483 of
the _Philosophical Transactions_; and of which I shall give a
description in the latter part of this Book, from the 3d Figure of the
3d plate.
[Sidenote: Fig. III.]
232. ’Tis plain that if the Ecliptic were more obliquely posited to the
Equator, as the dotted Circle ♈_x_♎, the equal divisions from ♈ to _x_
would come still sooner to the Meridian _Z0_♈ than those marked _A_,
_B_, _C_, _D_, and _E_ do: for two divisions containing 30 degrees, from
♈ to the second dott, a little short of the figure 1, come sooner to the
Meridian than one division containing only 15 degrees from ♈ to _A_
does, as the Ecliptic now stands; and those of the second quadrant from
_x_ to ♎ would be so much later. The third quadrant would be as the
first, and the fourth as the second. And it is likewise plain, that
where the Ecliptic is most oblique, namely about Aries and Libra, the
difference would be greatest: and least about Cancer and Capricorn,
where the obliquity is least.
[Sidenote: The second part of the Equation of Time.