In this construction, the wheels fixed on the sun's stern are 171, 178, 122, 154, 134, 97, and 63; the wheels at tached to the under faces of the radii vectores are 129. 126, 182, 166, 142, 126, and 76 ; and the small wheels in each train are made fast together in pairs, that revolve round as many studs on the upper faces of the respective radii x.ectores, and form the connexion between each adjoining train. In order that each pair of small wheels may have their direction of motion right, a small wheel is interposed in each train that does not enter into the computation. The arbor of the handle lies under, and parallel to the face of the table, and has a pinion 18, which turns a contrate wheel 61, on the arbor that ascends through the sun's stem, and forms part of his train ; and the days the week are indicated by a hand placed on the arbor of the handle at the front edge of the table. The heliocentric place of each planet is seen at any time on the large ecliptic circle surrounding the table, by holding a plumb line so that the eye, the planet, and the sun, are in the same straight line, when the plumb line is suspended above, and close to the edge of the table. The remote ends of the radii vectores are graduated, to show the mean anomaly, the equations of the centre, and heliocentric lati tudes of the corresponding planets, by the aid of hands fixed on the revolving pulleys respectively ; and, by these contrivances, the mean and equated anomalies are both rendered conspicuous, and illustrate even the formation of the planetary tables themselves; for the small arm at all times subtends the angle at the sun, which constitutes the grand equation belonging to the planet's angular dis tance from the perihelion position of the small arm, which distance is now called the mean anomaly.
Tellurian and Lunarium united.
A machine to explain the phenomena arising out of the joint motions of the earth and moon had long been a desi deratum, when, in the year 1805, the author of the present article computed all the requisite trains, and devised a plan for uniting them, on a scale of magnitude, and with a degree of correctness, that leaves nothing more to be wished for. Formerly the changes of day and night, and the vicissitudes of the seasons, were explained separately on a tellurian that had not the means of correctly indicating the time from clay to day, as the year advanced, in conse quence of the earth's rotations not being true solar days ; and the lunarium, when separately applied to the stand of the tellurian, exhibited indeed the phases, conjunctions, oppositions, longitudes, and latitudes of the moon, in a general way, but without reference to either time or place, so that it did not appear wip.a or wh r, the lunar pheno mena would be visibir, nor yet where the motions so cor rectly represented by the wheel work as the numbers more recently computed will give them. In fact, all the most interesting problems arising out of the various eccentric relative situations of the sun, earth, and moon, were thus incapable of being solved in any thing like a satisfactory manner. The occurrence of a solar or a lunar eclipse, for instance, might be pointed out as a phenomenon likely to• take place in a given lunation ; but the relative positions of the earth, sun, and moon, at the moment of such oc currence, and its visibility or invisibility to an inhabitant of a given country, were left entirely to conjecture ; the machine, however well computed and constructed in sepa rate portions, that required to be united, was quite incom petent to exhibit effects depending on a union of three different motions—on the earth's annual and diurnal mo tions, and on the moon's motion in its orbit ; which body is constantly varying both in velocity and the direction of its path. The machine, however, which we now proceed to describe, comprehends all the essential parts for showing the various phenomena resulting from a combination of these different motions, and, at the same time, points out the times and places of their occurrence in the most natu ral manner. We shall first give a synopsis of the wheel work employed in this curious machine, as we did of the planetarium, and afterwards point out how these wheels are disposed of, to perform their different offices in the most convenient and correct manner.
A perspective view of the principal parts of the tellurian and lunarium united in one machine, is given in Plate CCCCLX ; where some of the wheels that would other wise be concealed by the surrounding plates, bars, or bridges, are dotted, or withdrawn from their true posi tions, so as to be exposed to view. We propose to de
scribe the various wheels by the numerals that belong to their teeth, instead of letters of reference ; and the parts that support them will be seen from the situations in which they are placed, without a minute and tedious detail of particulars that will be obvious from an inspection of the figure.
Upon the plane of the circular table is screwed fast a broad rim of silvered brass, to receive the graduations that will be explained presently. A long bar of brass, braced by edge-bars, extends entirely across the table, and revolves round a solid stem of steel, made fast into the large wheel 269, under this bar, which may be called the annual bar, as it carries all the mechanism placed on it once round the said wheel and rim in each solar year, by means to be here after described. The steel stem passes through the centre of the table, and is kept close down by a tapped nut and collar under the table, so that the large wheel may be fixed in any position, as it regards the graduations on the circum scribed rim. On the upper end of the steel stem, above the annual bar, a contrate wheel, 62, is made fast, by a side screw passing through its piece of tube into the solid part of the steel, so that it may give motion to the small pinion 8, in contact with it, while the annual bar carries this pinion round it. The sun's stem is also carried round the central stem, by being erected a little out of the centre, bchind the central wheel 62, and a cr.mk-piece is attached near the sun's stem, to the remote end of the annual bar, which, therefore, partakes of its motion, and a silken thread stretched across the open part of the I rank- piecri, forms an index to all the divided circles and quacIrtiii•e viral on the face of the large brass rim attached to the table. Upon the nearer, or projecting end of the annual bar, are made fast several bridges and cocks, to support the remainder of the whcelwork, and to keep each wheel in its proper place of action; whicu we shall describe in separate trams, and in the order of their transmission of motion. handle is seen withdrawn from its squared arbor to the or the annual bar ; the horizontal arbor to which it belongs is con cealed, and carries a vertical wheel, 18, which drives the wheel 94 under the first large bridge, by acting with its connate teeth ; then the arbor 94, being pivoted into the said bridge above, descends through a hole cut in the an nual bar, and rests on a small cock under the said bar ; pinion, 10, fixed on this vertical arbor, drives the contrate wheel 26. the long arbor of which lies parallel to and under the .innual bar; till it reaches the teeth of the large wheel 269, %%ith which it is connected. That portion of the long arbu• just mentioned, which projects beyond the edge of the table, is displaced in the figure, together with the pinion 10. and small cock over it, which otherwise could not have been seen, nor easily comprehended; but the remainder of this arbor is concealed by the annual bar, as well as its pinion 10 that acts with the large wheel. This long arbor is carried by two cocks, one seen, out of its place, at the extreme end of the annual bar, and the other not seen, but fixed under the said bar, above the large wheel, in such a way that a screw with a milled head, seen within the cranked part of a small bridge carrying a long vertical stem, will draw up or let down the pinion borne by it, so as to put it into or out of action with the large wheel at option. Now, when the handle is inserted on its arbor of pinion 18, (concealed,) and turned round, the wheels 94 and 26 both commence moving by means of their impelling pinions; but the last pinion 10, meeting with a large wheel made fast to the table, cannot turn it round, but, as sufficient force is applied to the handle, the annual bar itself is obliged to move forward instead of the large wheel, and its revolution round the central stem is effected by the train in an exact solar year. Thus, in 5h. 48m. o 48'• the cranked index, attached to the annual bar, travels gradu ally over the graduations of the rim, as the handle gives the corresponding motion through the train ; and, what is important mportant consideration, no time is lost during this transmission of motion—the handle and the index have their motions contemporaneous. When our readers have seen how the annual bar is put into a steady regulated motion, they will easily conceive that the other wheels carried by it must also be put into their respective motions. We shall next explain how the motion of the handle is transmitted to the earth's axis.