If before the instrument is put into motion, the satellites of _Jupiter_ and _Saturn_ be brought into the same right line from their respective primaries, you will see them, as you turn the handle, immediately dispersed from one another, according to their different celerities. Thus one turn of the handle will bring the first of _Jupiter_’s Moons about ⁴/₇ part round _Jupiter_, while the second has described but ²/₇ part, the third but above ¹/₇, and the fourth not quite ¹/₁₆ part, each of its respective orbits. If you turn the handle until the hour index has moved 18½ hours more, the first satellite will then be brought into its former position, and so has made one entire revolution; the second at the same time will be almost diametrically opposite to the first, and so has made a little more than half of one revolution; the others will be in different aspects, according to the length of their periods, as will be plainly exhibited by the instrument. The same observations may be made with respect to the satellites of _Saturn_. The machine is so contrived, that the handle may be turned either way; and, if before you put it into motion, you observe the aspect (or situation with respect to each other) of the Planets, and then turn the handle round any number of times; the same number of revolutions being made backwards, will bring all the Planets to their former situations. I shall next proceed to particulars. _Of the Stations and Retrogradations of the Planets._ [Sidenote: _Retrograde Motion of the Planets._] The primary Planets, as they all turn round the Sun, at different distances, and in different times, appear to us from the Earth to have different motions; as sometimes they appear to move from West to East, according to the order of the signs, which is called their _Direct Motion_; then by degrees they slacken their pace, until at last they lose all their motion, and become _Stationary_, or not to move at all; that is, they appear in the same place with respect to the fixed Stars for some time together; after which they again begin to move, but with a contrary direction, as from East to West, which is called their _Retrograde Motion_; then again they become stationary, and afterwards reassume their direct motion. The reason of all these appearances is very evidently shewn by the _Orrery_. _Of the Stations_, &c. _of the Inferior Planets._ We shall instance in the Planet _Mercury_, because his motion round the Sun differs more from the Earth’s than that of _Venus_ does.