The Practical Astronomer / Comprising illustrations of light and colours--practical descriptions of all kinds of telescopes--the use of the equatorial-transit--circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy - Thomas Dick

On the axis ‘C’ at the bottom is wheel 86, which turns round in 365 days 5^h 48^m 49.19^s, this wheel impels a small wheel of 22 teeth, to which is made fast to wheel 67, both revolving together at the foot of axis B; wheel 67 drives a wheel of 72 once round in the period of 87 days, 23^h 14^m 36.1^s: this last mentioned wheel has a long tube, which turns on the steel axis A, and carries a horizontal arm with the planet Mercury round the sun in the time above noted.

VENUS’S PERIOD.

On axis ‘C’ is wheel 127, which drives wheel 47, to which is riveted a wheel of 77 teeth, which impels a wheel of 128 teeth on axis A, and causes it to make a revolution in 224 days, 16^h 41^m 31.1^s, and is furnished with a tube, which revolves over that of Mercury and ascends through the cover of the machine, and bears an arm on which is placed a small ball representing this planet in the time stated.

THE EARTH’S PERIOD.

The motion of the earth round the sun is simply effected as follows—the assumed value of axis ‘C;’ the ‘Yearly axis’ is 365 days 5^h 48^m 49.19^s; hence a system of wheels having the same numbers of teeth, or at all events, the first mover, and last wheel impelled must be equal in their numbers of teeth; in this machine three wheels are employed, thus; a wheel having 96 teeth is made fast to the Yearly axis C and of course moves round with it in a mean solar year, as above noted, this wheel impels another wheel of 96 teeth, on axis B, and this in its turns drives a third wheel of 96 teeth on axis A, and is furnished with a long tube which revolves over that of Venus, and ascends above the cover-plate of the machine, and bears a horizontal arm which supports a small terrestrial globe, which revolves by virtue of said wheels once round the sun in 365 days 5^h 48^m 49.19^s.

MARS’ PERIOD.

The revolution of this planet is effected as follows—a wheel of 140 teeth is made fast to the yearly axis C, and drives on axis B a wheel of 65 teeth, to which is fixed a wheel of 59 teeth, which impels a large wheel of 239 teeth on axis A once round the sun in 686 days 22^h 18^m 33.6^s, this last-mentioned wheel is also furnished with a tube which revolves over that of the earth, and carries a horizontal arm bearing the ball representing Mars, and causes it to complete a revolution round the sun in the period named.

THE ASTEROIDS. VESTA’S PERIOD.

The period of Vesta is accomplished thus, viz. On the Yearly axis C, is made fast a wheel of 36 teeth, which drives a wheel of 65 teeth on axis B, to which is fixed a wheel of 41 teeth, which impels a wheel of 83 teeth on axis A, once round in 1336 days 0^h 21^m 19.8^s: The tube of which last wheel ascends on that of Mars, and like the rest bears an arm supporting a ball representing this planet.

JUNO’S PERIOD.