Satellite Machine.
We have already given an account of the wheelwork of some of the machines that exhibit the revolutions of Ju piter's satellites by single pairs of wheels, and that pro duce the proper periods nearly ; but we have reserved to this place an account of a machine, into which a train of wheels is introduced for each separate satellite, and which produces all the requisite motions for not only explaining, but even computing, the occurrence of the various Jovian phenomena, with a degree of exactness that is truly sur prising. The machine in question was contrived and con structed in the year 1805, by the Rev. Dr. W. Pearson, and may either be used as a portable machine, without re ference to the motion of Jupiter and the earth, or may be applied to the stand of the Tellurian and Lunarium united, when some of its parts are dismounted, and other appen dages substituted. We propose to describe this machine first in its detached state, mounted on a small tripod, with out the motions of Jupiter and the earth ; and also as form ing a more extended piece of mechanism, acting in con junction with the trains that give motion to the two pri maries, Jupiter and the earth. Fig. 1. of plate CCCCLXI. is a section of a cylindrical brass box, containing the wheelwork that constitutes the trains for producing the respective revolutions of the four satellites, as they regard Jupiter seen from the earth. The different arbors are placed in a straight line, that none of the wheels or pin ions may be concealed behind one another ; but Fig. 2, which represents a portion of the circular cover, and ex plains the calliper, will convey a clear idea how the wheels are placed in the interior of the box, so as that each pair shall be situate properly for clue action. If we begin with the handle, we shall be able to trace the transmission of motion through the separate trains to each satellite; and, as in our preceding descriptions, if we use the nume rals belonging to the respective wheels, instead of letters of reference, the drawing will be less incutnbered. The first pinion 11, Fig. 3. is fixed on the horizontal arbor of the handle, and the tune 01 its turning round is assumed to be a solar day ; this impels another similar pinion 11 on a vertical axis, through the medium of a wheel 47, of which we shall take no farther notice at present, than that its teeth are formed to act with both pinions, by being rounded on the edge, and also 011 the face of the wheel; the latter pinion, therefore, revolves also in a solar day, and carries the hour-hand on its upper pivot, pointing to the hour-circle on the cover: this second pinion 11 ap pears in the figure removed almost the whole length of the section of the box from the weekly arbor, though in the box it reaches wheel 77, when brought round into its place depending on the calliper, and drives it round, together 77 with its arbor, in or 7 days. This weekly arbor, the upper pivot of which carries a hand to point out the seven days of the week, is common to four other driving wheels, ranged uric above another, namely, 57, 29, 29, and 83, all which are fast to the said weekly arbor : between this ar bor and the centre of the box, but drawn a little to one side, is made fast a steel cylindrical stem, rising perpendi cularly from the bottom of the box, round which stem four pairs of wheels separately revolve with appropriate velo cities, being respectively impelled by the tour wheels on the weekly arbor already specified : the lower wheel in each pair is driven, and the upper one is a driver, giving motion to a fourth wheel, attached to a revolving tube in the centre. Hence it is not difficult to perceive, that the
four concentric tubes, that carry the bent arms of the sa tellites, have each the fourth or last wheel of its own train attached to its lower extremity ; and that all the periods are separately produced by as many trains of four wheels each, acting on a uniform system ; the second and third wheels in every train being pinned together, and at liberty to revolve together round the coainnni fixed stem. The little ball, which represents is small enough to be taken as unity in the scale of distances given to the arms ; but a conical piece of brass wire may be inserted on tne bearing stem, instead of Jupiter's ball. with notches made at the under side for the small satellites to pa.s through, at the times of their falling into Jupiter's shadow, whole a paper screen attached to the box receives the shadows of the moving small bodies, and exhibits the various appear ances occasioned thereby, while a steady lamp, of A rgand's construction, properly adjust d, is made a substitute for the sun. The train which gives motion to the annual hand, that indicates the months, remains yet to be des cribed ; and as its only use is to regulate this hand, wheels of moderate dimensions, such as Feiguson employed, are chosen for effecting this purpose, without regard being had to extreme accuracy. On the diurnal vertical arbor is fixed the pinion 16, that drives the contiguous wheel 50 round a s "all stud descending from the cover ; then the pinion 7, made fast to the wheel 50, and revolving with it, impels the wheel 69 round a similar small stud under the cover with its attached pinion 7; and, lastly, this latter 7 turns the last wheel 83 and its arbor along with it, that bears the annual hand, in the requisite period, namely, in a solar year. Thus each turn of the handle gives the pro portionate quantum of motion to each oldie four satellites and three indexes, and these motions are all performed with such precision, that when the machine is once ad justed for the respective places of the arms and indexes, no new rectification will be necessary for several centuries back, or to come. The subjoined table contains all the particulars necessary for affording full information as to the dimen,ions and value of the trains contained in the box, w hien are all that are required when the box is mount ed on a small tripod, as a portable machine.