Thomas Jefferson Papers

From Thomas Jefferson to Robert Patterson, 16 October 1802

To Robert Patterson

Washington Oct. 16. 1802.

Dear Sir

The inclosed is merely the letter of form communicating the paper it covers to the society. but I promised Capt Groves to write you a private & more particular one. he has proposed a new method of observing the eclipses of Jupiter’s satellites at sea. you will percieve that he is not expert at explaining his ideas. he has invented an instrument too for making the observations, but what are it’s advantages or disadvantages I have not had time to examine. his proposition can be fully explained by the use of an instrument we already possess, that of Hadley’s sextant. instead of the small telescope sometimes fixed to that, substitute one of sufficient power to shew Jupiter’s satellites. perhaps a reflector would be more convenient than a refractor of equal power. take your observation, at sea, by drawing the planet & satellites down to or near the horison, in which situation, the body being erect can preserve it’s position by humoring the motion of the ship and have a steady view of the immersion or emersion of the Satellite. this seems to be a substitute for the Marine chair, and being a simple, easy & cheap thing, instead of a complicated, expensive & bulky one, several observers may act at the same time, the better to ascertain the instant of immersion. for the true time of the immersion he depends, as the marine chair does, on the time keepers in use. Capt Groves is not a man of science, & does not perfectly know how to estimate the merit of his invention. I told him I believed it would be within the usual course of the proceedings of the society to refer his paper to a committee, who would report their opinion & explain the degree of usefulness of his proposition. this is precisely what he wishes, for being very poor, he is anxious to make from it whatever it is worth. should I have mistaken the usual course of the society in supposing they would give an opinion on the merit of the proposition, then I would ask of you to favor me with a private statement of your view of it, to be communicated to him. to these favors I would sollicit that of dispatch to be added because he means to stay here until he learns the result, which in the very low state of his finances is not convenient to him. Accept my friendly salutations and assurances of high respect.

Th: Jefferson

RC (PPAmP); at foot of first page: “Mr. David Patterson.” PrC (DLC); TJ corrected Patterson’s first name in ink at foot of first page. Enclosures: (1) TJ to Patterson, 16 Oct.: “Dear Sir I inclose you a paper recieved from the hands of Capt Matthew C. Groves of Massachusets, wherein he proposes a more convenient method of observing the eclipses of Jupiter’s satellites for the purpose of ascertaining longitude at sea, than he supposes to have been hitherto practised. I communicate it to the society at his request, and tender you the assurances of my great esteem & respect” (PrC in DLC; at foot of text: “Mr. Robert Patterson. one of the V.P. of the A.P.S.”). (2) Description by Groves of “a new mode of observing the Eclipses of Jupiter’s Satellites &c.,” not found; presented to the American Philosophical Society in a meeting on 5 Nov. and referred to Patterson, who gave a report on Groves’s paper in a meeting on 18 Nov. (APS description begins American Philosophical Society description ends , Proceedings, 22, pt. 3 [1884], 327, 328).

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