I mentioned to Baron Humboldt my proposition for taking lunar observations at land without using a time piece. he said there could be no doubt of it’s exactness, but that it was not new, that even De la Caille had proposed it and De la lande had given all the explanations necessary for it, I think he said in his 3d. vol. I have not the book here but presume you can consult it in Philadelphia and will think it adviseable to do so before you address a paper to the P. Society on the subject. altho’ the idea was original with myself, yet if it is already known there is no occasion to repeat it.

I would wish to get a gunner’s brass rule, which are to be had in the mathematical shops of Philadelphia. they are 12. I. long, shutting to 6. I. and have points like caliber compasses for taking the caliber of balls and guns. I have seen scales like the 6. I. scales in the surveyor’s case of pocket instruments, which were 12. I. and even 2. f. long all in brass having in every respect the same things engraved on them as the1 common platting scale. I should be glad of one, if you can find one in the shops. the shop keeper will doubtless set these things down to me on an assurance that as soon as I know the amount I will remit it to him. indeed if you could open a correspondence for me with some honest dealer in mathematical instruments, I should be glad to have one to whom I could apply occasionally for what I want in that way. Accept my friendly salutations and assurances of esteem.