Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematicsFerguson, James
Science
Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematics
Ferguson, James
Astronomy -- Early works to 1800
| 29 | 8 13 | 8 56 | 0 22 | 1 |
| 30 | 8 24 | 8 46 | 0 0 | 0 |
+---------+--------+--------+--------+--------+
| 2d Q. | ♍ | ♌ | ♋ | Deg. |
| 4th Q. | ♓ | ♒ | ♑ | |
+---------+--------+--------+--------+--------+
| _Sun slower than the Clock in_ |
+---------------------------------------------+
[Sidenote: Fig. III.]
230. This part of the Equation of time may perhaps be somewhat difficult
to understand by a Figure, because both halves of the Ecliptic seem to
be on the same side of the Globe; but it may be made very easy to any
person who has a real Globe before him, by putting small patches on
every tenth or fifteenth degree both of the Equator and Ecliptic; and
then, turning the ball slowly round westward, he will see all the
patches from Aries to Cancer come to the brazen Meridian sooner than the
corresponding patches on the Equator; all those from Cancer to Libra
will come later to the Meridian than their corresponding patches on the
Equator; those from Libra to Capricorn sooner, and those from Capricorn
to Aries later: and the patches at the beginnings of Aries, Cancer,
Libra, and Capricorn, being also on the Equator, shew that the two Suns
meet there, and come to the Meridian together.
[Sidenote: A machine for shewing the sidereal, the equal, and the solar
Time.
PLATE VI.]
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
Public-domain text, read in full here on John Shaqi.
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