I recieved last night your favor of Dec. 17. as I had before done that of Dec. 5. I find nothing surprising in the raining of stones in France, nor yet had they been mill-stones. there are in France more real philosophers than in any country on earth: but there are also a greater proportion of pseudo-philosophers there. the reason is that the exuberant imagination of a Frenchman gives him a greater facility of writing, & runs away with his judgment unless he has a good stock of it. it even creates facts for him which never happened, and he tells them with good faith. Count Rumford after discovering cold to be a positive body will doubtless find out that darkness is so too. as many as two or three times during my seven years residence in France, new discoveries were made which overset the whole Newtonian philosophy; two or three examples happened of spontaneous combustion of the living human body, of houses &c. in all these cases the evidence of nature, derived from experience, must be put into one scale, and in the other the testimony of man, his ignorance, the deception of his senses, his lying disposition &c. and we must see which preponderates.

I expect to be authorised by Congress to explore and ascertain accurately the geography of the great rivers running into the Missisipi & Missouri, in order to fix their course & their sources, because their sources are the points which give the contour of what will now be the US. and having these & the whole course of the great rivers taken astronomically we have an accurate outline & skeleton which can be filled up with details hereafter. I should think of one party to go up the red river, & from the source of that to the source of the Arkansa, & down that. another up the Padoucas & down the Panis &c. I should consequently want 2 or 3. such men as Capt. Lewis at about 4. or 5. D. a day: perfectly equal to take the observations of longitude & latitude, & otherwise well qualified. if in your travels you have had experience of such characters, I will thank you to inform me of them. Accept my friendly salutations & assurances of esteem.