_Light is propagated from luminous Bodies in time, and spends about
seven or eight Minutes of an Hour in passing from the Sun to the Earth._
This was observed first by _Roemer_, and then by others, by means of the
Eclipses of the Satellites of _Jupiter_. For these Eclipses, when the
Earth is between the Sun and _Jupiter_, happen about seven or eight
Minutes sooner than they ought to do by the Tables, and when the Earth
is beyond the Sun they happen about seven or eight Minutes later than
they ought to do; the reason being, that the Light of the Satellites has
farther to go in the latter case than in the former by the Diameter of
the Earth's Orbit. Some inequalities of time may arise from the
Excentricities of the Orbs of the Satellites; but those cannot answer in
all the Satellites, and at all times to the Position and Distance of the
Earth from the Sun. The mean motions of _Jupiter_'s Satellites is also
swifter in his descent from his Aphelium to his Perihelium, than in his
ascent in the other half of his Orb. But this inequality has no respect
to the position of the Earth, and in the three interior Satellites is
insensible, as I find by computation from the Theory of their Gravity.