Thomas Jefferson Papers

To Thomas Jefferson from Andrew Gwin, 26 March 1798

From Andrew Gwin

Philadelphia March the 26th. 1798

The great attention your Excellancy has paid to My Universal quadrant and the trouble you have taken in writing to Virginia does Me honour beyond Expression and fully Convinces me of the great desire you have to encourage aney Usefull discoveries. Mr. Maddisons letter I have carefully examined but I find you did not give him aney directions Respecting the elevation of the Needle but I wish him to make a second trial With his diping needle and to be governed by the directions—first—let the horizontal Motion be confined: so that the instrument May be placed either: North-or-south—East-or-West then let the Needle be placed East and West and brought to nearly a true balance the North end rather the heaviest then turn the South end of the needle to the true North point let attention be paid to the: Degree of elivation on the arch where the Needle is checked by the polar attraction—the South Virtue of the Magnet being much inferior in Strength to that of the North that its power except when verry highly touched is not Equal to hold the Needle Stationary for More then 30” Seconds of time but the Magnetic Check is Easily percived if his needle does not hing two heavy on its axes he will find it to agree with the Latitude of the place of exhibition—Note—the instrument Must be kept in motion: and he will find the polar Check at the true Mile of Latitude—

My instrument is not yet Compleated but I have got the arch Devided to Degrees & half Degrees and to a Certanty the Needle cuts to a Mile the Lattitude of this City. My needle I have brought to Such perfection as to remain statioanary to the true polar attraction. I only now wait ain opertunity to give it a fair tryel at Sea—The inclosed is a Certificate of a discovery which I Made January last and concive it will be of the gratest utility to Navigation—the principles of which I wish to Communicate to you if agreeable—I also inclose Mr. Maddisons: letter. be pleased to return the Certificate.

I am respectfully Your Excellencys Most Obt. Servt.

Andrew Gwin

RC (DLC); endorsed by TJ as received 27 Mch. 1798 and so recorded in SJL. Enclosure: Bishop James Madison to TJ, 13 Mch. 1798. Other enclosure not found.

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