Part 34

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Footnote 139:

The Hon. Thomas Penn, of Stoke-Poges, in Buckinghamshire, heretofore one of the Proprietaries of the former province of Pennsylvania. This gentleman was then usually styled, in Pennsylvania, “The Proprietor.”

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His next letter to Mr. Barton, covering the promised Account of his Orrery, is dated the 27th of March, 1767: and this, it will be perceived, is very nearly a year before a description of it was communicated to the American Philosophical Society in Philadelphia. In this letter, he says—“Rowning’s opinion of Orreries pleases me more than any thing I had met with before. The idea of his imaginary machine naturally presents itself to persons conversant in Astronomy; but, if actually made, it could not answer the purpose, unless prodigiously large,—which I presume is the reason it has never been done.

“I send you a description of my imaginary machine: the foundation of it is now laid; and I hope that part of it, containing the mechanical Astronomy of the Moon, will be finished some time this spring: then we shall be able to judge, whether my abilities are equal to the undertaking.”

The “Description” here referred to, in Mr. Rittenhouse’s own hand-writing, is new before the writer of these Memoirs; and is thus endorsed by the Rev. Mr. Barton—“Original Description of Mr. Rittenhouse’s Orrery, first communicated to Thomas Barton.”—For the satisfaction of those, who may not have an opportunity of seeing the American Philosophical Society’s Transactions, in which this short account of the Orrery was afterwards published; and, as this original description of it differs somewhat from the printed one, it is presumed that the introduction of the former into this work, will not be unacceptable to the reader.

The impossibility of conveying to the mind of any one, even the most intelligent and skilful, by means of either any delineation upon paper in the nature of a diagram, or by words, an adequate idea of so complex and multiform a machine as the one now about to be described, will instantly be conceived. Indeed no description, alone, can render the nature of its construction, and the many curious and useful purposes it is capable of answering, perfectly intelligible to the most scientific Astronomer. Mr. Rittenhouse’s very concise description of his Orrery will, therefore, necessarily be found defective: it is thus worded by himself.

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“DESCRIPTION OF A NEW ORRERY.

“This Machine is intended to have three faces, standing perpendicular to the horizon: that in the front to be four feet square, made of sheet-brass, curiously polished, silvered, and painted in proper places, and otherwise ornamented. From the centre arises an axis, to support a gilded brass ball, intended to represent the Sun. Round this ball move others, made of brass or ivory, to represent the Planets: They are to move in elliptical orbits, having the central ball in one focus; and their motions to be sometimes swifter, and sometimes slower, as nearly according to the true law of an equable description of areas as is possible, without too great a complication of wheel-work. The orbit of each Planet is likewise to be properly inclined to those of the others; and their Aphelia and Nodes justly placed; and their velocities so accurately adjusted, as not to differ sensibly from the tables of Astronomy in some thousands of years.

“For the greater beauty of the instrument, the balls representing the planets are to be of a considerable bigness; but so contrived, that they may be taken off at pleasure, and others, much smaller, and fitter for some purposes, put in their places.

“When the Machine is put in motion, by the turning of a winch, there are three indexes which point out the hour of the day, the day of the month, and the year (according to the Julian account,) answering to that situation of the heavenly bodies which is then represented; and so continually, for a period of 5000 years, either forward or backward.

“In order to know the true situation of a Planet at any particular time, the small set of balls are to be put each on its respective axis; then the winch to be turned round until each index points to the given time. Then a small telescope, made for the purpose, is to be applied to the central ball; and directing it to the planet, its longitude and inclination will be seen on a large brass circle, silvered, and properly graduated, representing the zodiac, and having a motion of one degree in seventy-two years, agreeable to the precession of the equinoxes. So, likewise, by applying the telescope to the ball representing the earth, and directing it to any planet,—then will both the longitude and latitude of that planet be pointed out (by an index and graduated circle,) as seen from the earth.

“The two lesser faces are four feet in height, and two feet three inches in breadth. One of them will exhibit all the appearances of Jupiter and his Satellites—their eclipses, transits, and inclinations; likewise, all the appearances of Saturn, with his ring and satellites. And the other will represent all the phænomena of the moon, particularly, the exact time, quantity, and duration of her eclipses—and those of the sun, occasioned by her interposition; with a most curious contrivance for exhibiting the appearance of a solar eclipse, at any particular place on the earth: likewise, the true place of the moon in the signs, with her latitude, and the place of her apoge in the nodes; the sun’s declination, equation of time &c. It must be understood, that all these motions are to correspond exactly, with the celestial motions; and not to differ several degrees from the truth, in a few revolutions, as is common in Orreries.

“If it shall be thought proper, the whole is to be adapted to, and kept in motion by, a strong pendulum-clock; nevertheless, at liberty to be turned by the winch, and adjusted to any time, past or future.”

“N. B. The diurnal motions of such planets as have been discovered to revolve on their own axes, are likewise to be properly represented; both with regard to the Times, and the situation of their Poles.”

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The foregoing is a literal copy of the original manuscript; and such readers of this article as may think proper to compare it with the printed description of Mr. Rittenhouse’s Orrery, communicated to the American Philosophical Society by Dr. Smith, on the 21st of March 1768, and contained in the first volume of that Society’s Transactions, will find some (though, on the whole, not very essential) differences, in the two descriptions. The concluding paragraph, indeed,—designated, in each, by a N. B.—is materially variant in the two: and it appears, by its having been announced in the published (and later) account of this machine, that, “the clock part of it may be contrived to play a great variety of Music,” (a suggestion wholly omitted in Mr. Rittenhouse’s original communication, made to the Rev. Mr. Barton,) that the philosophic Artist had been afterwards induced, in one particular at least, “to comply with the prevailing taste.” But this may be readily accounted for: our artist had previously made some extremely curious and beautiful Time-pieces, to each of which was attached the mechanism of a Musical Clock, in addition to a limited Planetarium, in miniature. These were in the hands of gentlemen of respectability and taste: and they were much and generally admired, as well for the great ingenuity displayed by the constructor, in these combined and pleasing operations of his machinery, as for the superior accuracy and beauty of the workmanship; qualities eminently conspicuous in all his mechanical productions.

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Footnote 140:

This design was, however, finally abandoned.

Footnote 141:

One of these valuable clocks, which is of a large size, with an accurate little planetarium attached to its face and placed above the dial-plate, was made for the late Mr. Joseph Potts, of Philadelphia county, who paid for it, as the writer is informed, six hundred and forty dollars. In the spring of the year 1774, it was purchased by the late Mr. Thomas Prior, of Philadelphia; to whom, it is said, general Sir William Howe made an offer of one hundred and twenty guineas for it, shortly before the evacuation of that city, in 1778. It is also said, that Don Joseph de Jaudenes, late minister of Spain to the United States, offered Mr. Prior eight hundred dollars for this clock, with a view of presenting it to his sovereign. Mr. Prior, however, retained it until his death, in the spring of the year 1801: after which, it passed through two other hands, successively, into the possession of Professor Barton, of Philadelphia, whose property it now is.

Footnote 141a:

The area of the face of the dial plate is twenty inches square, and the motions and places of the planets of our system are represented on a circular area of eight inches in diameter.

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It appears, that when Mr. Rittenhouse sent the foregoing description of his projected Orrery to Mr. Barton—that is to say, on the 27th of March, 1767—the “foundation” of it was “laid.” But, notwithstanding his earnest wishes prompted him to the utmost diligence, in his exertions to finish it, many circumstances concurred to retard its completion. The magnitude of the undertaking—the multiplicity of the work—and, perhaps, the difficulty of sometimes readily procuring, even from Philadelphia, the necessary materials,—all conspired, to prevent as early a completion of the machinery as he had anticipated: and, added to these causes of unavoidable delay, was the yet unabandoned pursuit of his professional business.