I have received your Favour of July last as well as the valuable Books you were so good as to send to the Care of Mr. Wythe. I cannot sufficiently express the obligations I feel myself under for these continued Marks of your Kindness. The Books were such as have afforded me the greatest Entertainment as well as Instruction. Fourcroy’s Chymistry was a great Acquisition to me, especially as he has concentered more of the modern Discoveries than any other general Treatise I have seen.—Your Notes on Virginia I shall always highly esteem not only on Account of their intrinsic worth, but also, the Hand from which they came. I know not how your Confutation of a certain opinion so derogatory to America, may be received in Europe, but, to my Mind, it is compleat. I hope your Notes judiciously distributed among our young Men here, will tend to excite the spirit of philosophical observation amongst us.—Never was there a finer Range for the Exercise of such a Spirit, than this Country presents, and it would certainly be fortunate, if some Man of Genius would turn his Attention not only to the productions of our Continent, but to the Continent itself. Perhaps among the different sources of Satisfaction, which you must experience from your patriotic Exertions, it will not be the least that you have been foremost in exciting among your Fellow Citizens, so laudable as well as so necessary a Spirit.—Your Observations upon the Disruption of the Blue Ridge by the Potowmac, called to my Mind, another Vestige of Water, which I do not know that any one has yet mentioned. It is a Fact, which I have myself observed, that the No. Side of the Blue Ridge and the So. Side of the Allegany, are still in a great Measure deprived of Mould. You see scarce any where, along those Sides, but little of that Soil which is necessary for Vegetation. For the most Part, they present only naked Rocks, whereas on the So. Side of the Blue Ridge, and No. Side of the Allegany, the reverse takes Place: in general a fine rich Mould, and Vegetation in the greatest Luxuriancy. Doth not this Fact indicate, that the Space between those nearly parallel Ridges, has been swept by an immense Current of Water, or has contained a vast Body of Water, which in it’s Recess, deprived the opposite sides of their Soil, and thus left them in a similar State. A Part of this general Mass of Water, probably found it’s Vent at the Gap you have so well described. If this Conjecture be not just, why should we find such a Similarity between the Sides of Mountains, whose Exposure is the reverse of each other.—That our Mountains have experienced the powerful Agency of Water, no one can doubt who has examined the Sides either of single Mountains, or of Mountains which are near to each other. But, from whence the Waters came, or whether what is now Continent was not once the Bed of the Ocean, I do not pretend even to conjecture. I agree with you entirely, that it is better to beleive Nothing, than what is wrong.

I should be much obliged, if in your next Letter which you may favour me with, you would be so good as to inform me, of the best Treatise on Conchology. I wish to see the Nat. Histy. of this lower Country somewhat inquired into.

Among the different curious Articles of litterary Information, with which your last Letter gratified me, I was particularly struck with that which mentions the Demolition of the Newt. Theory respecting the Rainbow. If this be the Case, it will afford a remarkable Instance of the Necessity of extreme Caution in reasoning even from Facts, as in the Application of those particular Laws of Nature which may be investigated to the Solution of general Phænomena. But for my own Part I cannot but think most of the Phænomena of the Rainbow are so beautifully and satisfactorily explained by that Theory as still to doubt whether the Abbé will have the Merit of its entire Demolition. One Fact you mention I believe has been observed by many, Viz. that of seeing one end of the Bow nearer than the other. This appears to overthrow the Idea that the Eye is placed in the Apex of one Cone formed by the Rays. But granting that the present Theory may not account satisfactorily for all the Appearances of the Bow, and that some Phænomena may occur which seem to oppose it, yet I question whether it will follow that every other Part of the Theory will fall.—I am inclined to believe that the circular Appearance is not sufficiently accounted for, and had my doubts increased by an accidental Experiment, just before the Receipt of your Letter. It is perhaps one, which trifling as it may appear at first View, still deserves some Attention. Having a fine Tooth Brush in my Hand, which I had dipped in Water, and then flirting it through my Fingers, the Sun shining and my Position favourable, I was struck as with a beautiful Appearance of two Bows. But what particularly excited my Attention was the apparent dipping of one of the Legs—not unlike, probably, what you observed in the Valley near Monticello. The Experiment may easily be made and indeed somewhat similar Experiments are mentioned by others, tho’ I do not know of any so well calculated to give Satisfaction, I mean in exhibiting the Bow, and in shewing that the Colours do not take a real circular Form—one part of the Bow will also be nearer to you than another, and the Difference of Distance may be easily ascertained. Yet I am not willing to give up the Theory altogether, tho my Attachment to Systems is very far from being strong. An Error removed, if not an Addition to Knowledge, certainly prepares us for the Acquisition of it.

The Thermom. here has this winter been at 9. in Jany. 1st Feby. at sun rise it was at 14—the 2d. at 10, same time of Day.

I hope by my next to be able to communicate to you some Astronom. Observations, as a small Return for your supply of the Conn. de Temps.

We have no litterary Returns to make to you. It seems to be our Fate as yet to look to Europe for the Lights of Science.—Politics engross the Attention of almost every one. The new continental Government which has been proposed, and which has so greatly divided the Minds of the People, affords a strong Incitement to political Speculation.—Whether it’s operation will be happy for America seems problematic.

Your Nephew Mr. P. Carr is attentive to his Studies and, I hope will at least establish a good Foundation to build upon. Be assured, Dear Sir, of my sincere Desire to be useful to him—and of the great Esteem & Regard with which I am Your Friend & Servant,