Your favour of the 18th. has just come to hand, and the first leisure hour I have, shall be employed in furnishing Mr. Churchman with the information he is requesting.

Mr. Churchman is at least entitled to credit for his perseverance, but his theory is unfortunately entitled to none, because it cannot be rendered useful, even admitting the principles to be correct. It is well known to every practical astronomer, and mariner, that neither the amplitude of the sun, or of a star, can at all times be determined within 10, or 15 minutes of a degree of the truth, and frequently on much more; but even 10 minutes in those seas, where the magnetic, and true meridians, are nearly parallel, would produce an error of 5 or 6 degrees in the longitude.

The magnetic variation is affected by so many causes that it is rendered too complex, for the quantity to be determined with the necessary exactness in different parts of the world (to answer any valuable purpose) by any mode of calculation with which we are acquainted.

The documents you are requesting were left with Mr Galliten after you left the City of Washington last July, and I expected they had been handed to you long before this.

Some weeks ago I forwarded to the President about 32 pages of manuscript remarks,1 to accompany a map2 of the Mississippi from the mouth of the Ohio, down to the gulf of Mexico, the whole southern boundary of the United States, and of west Florida. The map should have been sent with the remarks but from its size, it is difficult to find any person willing to take charge of it. I have endeavoured to render it as correct as possible, that it may serve as a basis for the perfection of the geography of our southern country. It is probably the last scientific work I shall ever have to offer to the Public—my present employment which occupies the whole of my time being unconnected with science.3

Wishing you health in executing the arduous duties of your station I have the Honor to be with great sincerity your friend and Hbl. Servt.