“I would have you pursue your Orrery in your own way, without any regard to an ignorant or prevailing taste. All you have to study is truth, and to display the glorious system of Copernicus in a proper manner;—and to make your machine as much an original, as possible. I beg you will not limit yourself in the price. I am now perfectly convinced, that you can dispose of it to advantage; and should be sorry you would lose one hour more in fears or doubts about it. In fact, I have laid such plans for the disposal of it, that I have almost a moral certainty of having a demand for more than one of the kind. I have not time to write you as fully as I could wish, as the transcribing from Rowning has detained me so long, and I am this moment setting out for Caernarvon. “My letter to the Proprietor[139] is delayed, till I can send him the account of your design, which you are pleased to promise me. You say you have “a specimen” in hand: I should be glad to know what it is. “I shall not neglect the things you mentioned to me, as I shall always receive a pleasure in serving you.... She joins me in love to father, mother and all friends.—I am, in haste, dear Davy, your very affectionate friend and brother, “THOMAS BARTON. “P. S. Forgive this wretched scrawl—I have not time to examine whether I have committed any errors in copying Mr. Rowning. “I beg leave to recommend Huygens’, Cotes’, Helsham’s, and Power’s Philosophy to you. You will be much pleased with them. ----- Footnote 138: See _A Compendious System of Natural Philosophy_, &c. by J. Rowning, M. A. part iv. chap. 15. ----- “I wish you would purchase Bion’s Description of Philosophical and Mathematical Instruments, &c.” “MR. DAVID RITTENHOUSE.” ----- 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.” ----- 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.”