The works of that late most excellent philosopher and astronomer, Sir George Wharton, bar. collected into one volume / by John Gadbvry ...

Of the Aequation of time, in respect of the Inequality of Natural Days.

THe Natural Days are two ways considered, Aequal and Inequal.

The Aequal are the mean days, consisting of one whole Revolution of the Aequator, and an additament of so much time, as is answerable to 59′. 8″. 19‴ 45''''. (the mean motion of the Sun in one Day.)

The Inequal are the true or apparent days, which consist of so much time as the Revolution of the Aequator is made in, with an additament of so much time as agrees to the true motion of the Sun in one Day.

The Inequality therefore of these Days arises from this Inequal additament, and that for two causes re∣spectively.

1. The first of which is the Inequal Motion of the Sun in the Ecliptique, for the Sun being moved in an Eccentrical Orb, it so happens, that in equal spaces of time, he describes inequal Arches of the Ecliptique: and therefore it must needs follow that the Ascentions of the Aequator, or additaments agreeing thereunto are also inequal: And this Experience it self tells us; for the Sun runs through one half of the Zodiack, viz. the six Northern Signs, ♈. ☿. ♊. ♋. ♌. ♍. not in less time than 186 days, and about 6 hours: but the other half, viz. the six Southern Signs, ♎. ♍. ♐. vs. ♒. ♓. in 178 days, and almost 22 hours.

2. The second is the Obliquity of the Zodiack, which causes an Inequality or difference (as well in a right, as Oblique Sphere) betwixt the Right Ascentions of the Aequator and Zodiack.

Whence it appears, that the difference betwixt an apparent, and a mean or Aequal day, is called the Aequation of Days; for that by this Aequation, the Natural mean days, are converted into the true or apparent.

Wherefore seeing that Inequal days cannot be the measure of equal motions, it is requisite that those Inequal days be converted to equal, (so oft as we intend to supputate the Equal motions by the Ephemeris) but contrary wise when we would reduce the Equal or mean Days to apparent or Inequal.