the periods of time in which the several planets make their revolutions round the sun or earth.

As from the proper revolution of the sun the solar year takes its origin, so from the proper revolutions of the rest of the planets about the earth, several sorts of years arise; such are the Saturnian year, which is defined by twenty-nine Egyptian years, 174 hours, fifty-eight minutes, equivalent in a round number to thirty solar years; the Jovial year, containing 317 days, fourteen hours, fifty-nine minutes; and the Martial year, containing 321 days, twenty-three hours, thirty-one minutes. With respect to Venus and Mercury, as their years, when judged of with regard to the earth, are almost equal to the solar year, so they are more usually estimated from the sun, the true centre of their motions; in which case the former is equal to 224 days, sixteen hours, forty minutes, and the latter to eighty-seven days, twenty-three hours, fourteen minutes.