Chromatius, however, the governor of Rome, construct ed a machine in the third century, which, probably, was intended to represent the Ptolemaic system ; it is record ed, both by St. Sebastian and St. Polycarp, as being a chamber composed of glass, ( on which was explained the knowledge of the heavenly bo dies, and in the construction of which two hundred pounds weight of gold was employed ; it is said to have had an ecliptic circle divided into twelve signs, and that the dif ferent phases of the moon were shown by mechanism; but how far this could be considered as a planetary ma chine does not appear: it has been affirmed, that the saints of that day, either from a supposed attaching to this representation of the heavens, or from the known value of the materials of which it was composed, took the liberty of converting the erection into some purpose more agreeable to their own wishes. Their veneration for the heavenly science yielded, probably, to their more powerful attachment to the building made with hands.
The celebrated Chinese astronomer Y•tang had a ma chine constructed about the year 721, which, according to Father Gaubil, contained'many wheels, put into motion by water, that gave motion to the sun, moon, and five planets, and indicated the ke or hundredth part of the Chinese day by pointers, cne for the day, and the other for the night ; this contrivance also gave notice of the arrival of the kr, by making a little image step forwards, and give an audible stroke on the face of a wooden board; which mechanism must have been anterior to the invention of clocks, except the clepsydra', or water-clocks, of which this may have been a specimen; for we find, down to the present day, an evident disposition, in the more scientific mechanics, to apply the maintaining and regulating powers of a clock to produce the recurrence of the clay of the month, of the moon's age and phases, and, occasionally, the motions of the planets or satellites, in addition to the indication of the current time. Ot a similar nature must have been the contrivance of William, the abbot of Hirsham, who, in the eleventh century, is said " to have invented a natural ho rologe in imitation of the celestial hemisphere," (naturale hor,logium ad est inplum celesta hari.+hheri' excogitasse.) Besides these, we read of various other horologes in the thirteenth, fourteenth, and fifteenth centuries, which have partaken of the joint consti uction of clocks and planetary machines ; one of which was given by one of the Sultans of Egypt to the Emperor Frederick 11. of Germany, in the year 1232. Another was made by the learned Abbot of St Albans, Richard of Wallinglord, which, Leland says, exceeded, in ingenious contrivances and expensive work manship, every other machine in Europe. And a third
was constructed by John Dondi, afterwards styled Ilorelo gins, from his great skill in horological mechanism. But the first, perhaps the only machine that exhibited the Ptolemaic system, was made by Heirlin, under the direc tion of the ingenious Werner of Nuremberg, about the year 1500. We are not, however, aware, that any particu lar description of this piece of mechanism has been re corded, so that we may gain access thereto.
Having arrived at the time when Copernicus, in oppo sition to all the prejudices of a long established opinion respecting the motion of the sun, made the earth a planet, and fixed the sun in her place, at the centre of what is now called the solar system, we might naturally have expectecl to meet with some variation in the structure of its me chanical representation ; particularly as clock-work had begun to be cultivated at that time ; but we find that new systems, how ever plausible, when proposed by humble in dividuals, are not suddenly adopted by prejudiced minds. The well known clock of Oronce Finee, in the library of the Pantheon at Paris, was constructed in several years after the demise of Copernicus, and yet shows the planetary periods on a supposition that the earth is placed in the centre, with the sun revolving between her and Mars, and carrying his secondaries, Mercury and Venus, along with hint. The periods are produced by wheelwork, with a degree of accuracy that does credit to the inventor ; and for the first time we find the period of the retrogression of the moon's node included. In a V • printed Recueil, No. —, in the library already mentioned, 68 it is stated, that the increase and decrease of the planetary velocities are alternately produced by the mechanism, as as well as the eccentricities, motions of the nodes and apogees, and deviations from the ecliptic ; all which are indicated on the different faces or dials of the machine.
Even so lately as in the year 1650, we are told by Schott, in his " Technica Curiosa," that P. Schirleus de Rheita constructed a planetarium, that represented all the true and mean motions of the pl nets then known, with their stations, retrogradations, &c. by means of wheelwork ac tuated by a water wheel, on a supposition that the sun is a planet, accompanied by Mercury and Venus as his sa tellites. Hence it is evident, that the true solar, or Co pernican system of the world, was not generally received at the middle even of the seventeenth century.