When _Mercury_ is in his superior conjunction (or when he is in a direct line from the Earth beyond the Sun) fasten a string about the axis of the Earth, and extend it over _Mercury_ to the ecliptic; then turning the handle, keep the thread all the while extended over ☿, and you will find it move with a direct motion in the ecliptic, but continually slower, until _Mercury_ has the greatest elongation from the Earth. Near this position, the thread for some time will lay over _Mercury_ without being moved in the ecliptic, tho’ the Earth and _Mercury_ both continue their progressive motion in their respective orbits. When _Mercury_ has got a little past this place, you will find the thread must be moved backward in the ecliptic, beginning first with a slow motion, and then faster by degrees, until _Mercury_ is in his inferior conjunction, or directly between the Earth and the Sun. Next this position of ☿, his retrograde motion will be the swiftest; but he still moves the same way, tho’ continually slower, ’till he has again come to his greatest elongation, where he will appear the second time to be stationary; after which he begins to move forward, and that faster by degrees, until he is come to the same position with respect to the Earth, that he was in at first. The same observations may be made relating to the motions of _Venus_. In like manner the different motions observed in the superior Planets may be also explained by the _Orrery_. If you extend the thread over _Jupiter_, and proceed after the same manner as before we did in regard to _Mercury_, you will find that from the time _Jupiter_ is in conjunction with the Sun, his motion is direct, but continually slower, until the Earth is nearly in a quadrate aspect with _Jupiter_, near which position _Jupiter_ seems to be stationary: After which he begins to move, and continually mends his pace, until he comes in opposition to the Sun, at which time his retrograde motion is swiftest. He still seems to go backward, but with a slower pace, ’till the Earth and he are again in a quadrate aspect, where _Jupiter_ seems to have lost all his motion; after which he again resumes his direct motion, and so proceeds faster by degrees, ’till the Earth and he are again in opposition to each another. [Sidenote: _Plate 3_. _Fig. 1_.]