The revolution of this planet could not be attained with sufficient accuracy from the period of a solar year—the period is engrafted on that of Saturn’s, thus, a wheel of 117 teeth is made fast to wheel 190 of Saturn, and consequently revolves in Saturn’s period. This wheel of 117 teeth drives a wheel on axis B, having 77 teeth, to which is fixed a wheel of 40 teeth, which turns on axis A, a large wheel of 173 teeth, whose tube ascends and revolves over that of Saturn, and carries a horizontal arm which supports a ball representing this planet, which is caused to complete its revolution by such a train of wheels in the period of 30589d 8h 26m 58.4s. Such is a brief description of the motions of this comprehensive and very accurate machine.
The axis A, on which the planetary tubular wheels revolve, performs a rotation in 25 days 10 hours, by virtue of the following train of wheels, 61/14 + 70/12 of 24 hours, that is, a pinion of 14 is assumed to revolve in 24 hours, and to drive a wheel of 61 teeth, to which is fixed a pinion of 12, which turns the wheel 70 in the period noted; to this wheel-axis, it is made fast, and by revolving with it, exhibits the Sun’s rotation.
DIURNAL HAND.
The machine is turned by a handle or winch, which is assumed to turn round in 24 hours, and from this rotation of 24 hours a train of wheel-work is required to cause the ‘yearly axis’ C, to turn once round in 365d 5h 48m 49.19s, which is effected in the following manner—viz, the train found by the process of the reduction of continuous fractions is 61/14 + 144/18 + 211/23 that is, in the train for turning the sun, the same pinion 14 turns the same wheel 61, and turns a pinion of 18 leaves, to which is fixed a wheel of 144 teeth, having a pinion of 23 leaves, which impels a large wheel of 241 teeth once round in 365.242236d or 365d 5h 48m 49.19s, this last-mentioned wheel of 241 teeth is made fast to the under part of the ‘yearly axis’ C at D, the handle having a pinion of 14 leaves therefore, and transmitting its motion through the above train, causes the yearly axis to revolve in the same period.
REGISTRATING DATES.
The planetarium is also furnished with a system of wheels for registrating dates for either 10,000 years past or to come, the arrangement is not shewn in the engraving (to prevent confusion) but it might be shortly described thus:—Near the top of the yearly axis is a hooked piece e, which causes the tooth of a wheel of 100 teeth to start forward yearly, consequently 100 starts of said wheel will cause it to revolve in 100 solar years, and it has a hand which points on a dial on the cover of the machine the years; thus for the present year this hand will be over the number 45. This last-named wheel of 100 teeth has a pin which causes a tooth of another wheel of 100 teeth to start once in 100 years, hence this last wheel will complete one revolution in 10,000 years, and it is for this purpose the former index or hand moves over a number yearly. The second index will pass over a number every 100 years—for the present year the second hand or index will be over the number 18, and will continue over it until the first index moves forward to 99, then both indexes will move at one time, viz., the first index to 00 on the first concentric circle of the dial, and the second index to 19, denoting the year 1900, and so of the rest. By the ecliptic being divided in a series of four spirals, the machine makes a distinction between common and leap years, and indicates the common year as containing 365 days, and the leap-year 366 days, by taking in a day in February every fourth year; thus for any given period for 10,000 years past or to come, the various situations and aspects of the planets may be ascertained by operating with this machine, and this for thousands of years without producing a sensible error either in space or time. This planetarium wheel-work is enclosed in an elegant mahogany box of twelve sides—is about 5 feet in diameter by 10 inches in depth; at each of the twelve angles, or sides, small brass pillars rise and support a large Ecliptic circle on which are engraven the signs, degrees and minutes of the Ecliptic—the days of the month, &c. This mahogany box with the wheel-work is supported by a tripod stand three feet in height, and motion is communicated to the several balls representing the planets by turning the handle as before described. A Planetarium of this complicated sort, costs sixty guineas.
The following is a tabular view of the wheel-work, periods, &c.
| Planets’ Names. | Wheel-work. | Tropical periods produced by the wheel-work. | True mean Tropical Periods of the Planets. | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| da. | ho. | m. | s. | da. | ho. | m. | s. | ||||
| Mercury | " | 22/85 + 67/72 | of a Year | 87. | 23. | 14. | 36.1 | 87. | 23. | 14. | 36 |
| Venus | " | 47/127 + 128/77 | " | 224. | 16. | 41. | 31.1 | 224. | 16. | 41. | 36 |
| The Earth | Prime mover | 96 + 96 + 96 | " | 365. | 5. | 48. | 49.19 | 365. | 5. | 48. | 49 |
| Mars | " | 65/140 + 239/59 | " | 686. | 22. | 18. | 33.6 | 686. | 22. | 18. | 34 |
| Vesta | " | 65/36 + 83/41 | " | 1335. | 0. | 21. | 19.8 | 1335. | 0. | 21. | 20 |
| Juno | " | 50/54 + 127/27 | " | 1590. | 17. | 35. | 2.7 | 1590. | 17. | 35. | 1 |
| Ceres | " | 130/123 + 30 | of Juno | 1681. | 6. | 17. | 22.4 | 1681. | 6. | 17. | 29 |
| Pallas | " | 81/122 + 119/79 | of Ceres | 1681. | 10. | 28. | 25.1 | 1681. | 10. | 28. | 42 |
| Jupiter | " | 94/44 + 111/20 | of a Year | 4330. | 14. | 39. | 35.7 | 4330. | 14. | 39. | 32 |
| Saturn | " | 129/17 + 190/49 | " | 10746. | 19. | 16. | 50.9 | 10746. | 19. | 16. | 52 |
| Uranus | " | 77/117 + 173/40 | of Saturn | 30589. | 8. | 26. | 58.4 | 30589. | 8. | 26. | 59 |
| The Sun’s Rotation | 61/14 + 70/12 | of 24 ho. | 25. | 10. | 0. | 0 | 25. | 10. | 0. | 1 | |
| The tropical period of the Earth round the Sun. | 61/14 + 144/18 + 241/23 " | 365. | 5. | 48. | 49.19 | 365. | 5. | 48. | 49 | ||
In the month of October last year, Dr. Henderson made a series of calculations for a new Planetarium for the use of schools. It shows with considerable accuracy for 700 days, the mean tropical revolutions of the Planets round the sun—the machine consists of a system of brass wheels peculiarly arranged, and is enclosed in a circular case three feet in diameter, the top of which has the signs and degrees of the ecliptic laid down on it, as also the days of the months, &c. This Planetarium costs only 45s. or on a tripod stand, table-high, 55s.; the machine is put in motion by a handle on the outside. To the teachers and others connected with education this Planetarium must be of great importance, for without a proper elucidation of the principles of astronomy, that of Geography must be but confusedly understood. This Planetarium is at present made by Mr. Dollond, 9, White Conduit Grove, Islington, London.
The Tellurian is a small instrument which should be used in connection with the Planetarium formerly described. This instrument is intended to show the annual motion of the earth, and the revolution of the moon around it. It also illustrates the moon’s phases, and the motion of her nodes, the inclination of the Earth’s axis, the causes of eclipses, the variety of seams, and other phenomena. It consists of about eight wheels, pinions and circles. A small instrument of this description may be purchased for about one pound eight shillings, as stated in the note, page 527.