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
243. The last Table but one, at the end of this Chapter, shews the Sun’s
place in the Ecliptic at the noon of every day by the clock, for the
second year after leap-year; and also the Sun’s Anomaly to the nearest
degree, neglecting the odd minutes of a degree. Their use is only to
assist in shewing the method of making a general Equation Table from the
two fore-mentioned Tables of Equation depending on the Sun’s Place and
Anomaly § 229, 241; concerning which method we shall give a few examples
presently. The following Tables are such as might be made from these
two; and shew the absolute Equation of Time resulting from the
combination of both it’s causes; in which the minutes, as well as
degrees, both of the Sun’s Place and Anomaly are considered. The use of
these Tables is already explained, § 225; and they serve for every day
in leap-year, and the first, second, and third years after: For on most
of the same days of all these years the Equation differs, because of the
odd six hours more than the 365 days of which the year consists.
[Sidenote: Examples for making Equation Tables.]
EXAMPLE I. On the 15th of _April_ the Sun is in the 25th degree of ♈
Aries, and his Anomaly is 9 Signs 15 Degrees; the Equation resulting
from the former is 7 minutes 23 seconds of time too fast § 229; and from
the latter, 7 minutes 27 seconds too slow, § 241; the difference is 4
seconds that the Sun is too slow at the noon of that day; taking it in
gross for the degrees of the Sun’s Place and Anomaly, without making
proportionable allowance for the odd minutes. Hence, at noon the
swiftness of the one Equation balancing so nearly the slowness of the
other, makes the Sun and Clocks equal on some part of that day.
EXAMPLE II. On the 16th of _June_, the Sun is in the 25th degree of ♊
Gemini, and his Anomaly is 11 Signs 16 Degrees; the Equation arising
from the former is 1 minute 48 seconds too fast; and from the latter 1
minute 50 seconds too slow; which balancing one another at noon to 2
seconds, the Sun and Clocks are again equal on that day.
EXAMPLE III. On the 31st of _August_ the Sun’s place is 7 degrees 52
minutes of ♍ Virgo (which we shall call the 8th degree, as it is so
near) and his Anomaly is 2 Signs 0 Degrees; the Equation arising from
the former is 6 minutes 41 seconds too slow; and from the latter 6
minutes 39 seconds too fast; the difference being only 2 seconds too
slow at noon, and decreasing towards an equality will make the Sun and
Clocks equal in the afternoon of that day.
EXAMPLE. IV. On the 23d of _December_ the Sun’s place is 1 degree 41
minutes (call it 2 degrees) of ♑ Capricorn, and his Anomaly is 5 Signs
23 Degrees; the Equation for the former is 43 seconds too slow, and for
the latter 58 seconds too fast; the difference is 15 seconds too fast at
noon; which decreasing will come to an equality, and so make the Sun and
Clocks equal in the evening of that day.
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