From Thomas McLean
Frederick County July 27th. 1802
Most Honored Citizen
My commerce with literary characters is so limited that I did not know of the existance of a Philosophical society at this time in any part of the United states,† else my first step would have been to enquire how I could convey to them the contents of my letter of May 2nd.: but this I would have done, without the most remote idea that my right to a patent was thereby forfeited; but if it should, I would prefer a transmittal of it to the society, because I am not in circumstance to use it. If I knew at what time to write, and in what manner to direct I would communicate a few things to the society which might be useful, such as the theory and principles of Optical glasses and Telescopes which might be of use in constructing the grand Telescope contemplated at Washington City. In Nicholsons Philosophy and the American addition of the Encyclopedia their Optics appear to me correct as far as the theory is therein ixplained, but that it remains unfinished because, they have not demonstrated that by the diameters of the reflectors and glasses and their focal distances, a Telescope may be constructed to any assigned degree of perfection—Example, a newspaper being placed at one mile distant required a Telescope that will represent it exactly at the distance of three feet: this is what I have not found in their Optics. If your attention to the general good forbids you to send me another line, I cannot complain, but if you can, it will be another cordial to one who has ever been desirous of your promotion and happiness.—
RC (DLC); addressed: “His Excellency Thomas Jefferson President of the United states”; franked; endorsed by TJ. Recorded in SJL as received 5 Aug.
GRAND TELESCOPE CONTEMPLATED AT WASHINGTON: despite calls for the construction of an observatory, first at Philadelphia and subsequently at Washington, those plans did not come to fruition until the 1830s and 1840s (John C. Greene, American Science in the Age of Jefferson [Ames, Iowa, 1984], 129, 138, 154).
NICHOLSONS PHILOSOPHY: William Nicholson, Introduction to Natural Philosophy, a commonly cited text on natural science; see Vol. 23:364; Vol. 30:594; Vol. 31:68; Vol. 32:180.
Often referred to as the AMERICAN encyclopedia, Thomas Dobson’s Encyclopaedia; or, A Dictionary of Arts, Sciences, and Miscellaneous Literature, which originally consisted of 18 volumes published at Philadelphia in 1798, was a revision of the third edition of the Encyclopaedia Britannica (Robert D. Arner, Dobson’s Encyclopaedia: The Publisher, Text, and Publication of America’s First Britannica, 1789–1803 [Philadelphia, 1991], x, 4, 30; Sowerby, description begins E. Millicent Sowerby, comp., Catalogue of the Library of Thomas Jefferson, Washington, D.C., 1952–59, 5 vols. description ends No. 4891; Vol. 29:440, 441n).