DEAR SIR,--I have been long, very long, without answering your favor of March 27, 1786, and since that I have received those of December 28, and by Mrs. Oster. The reason of this has been that the genius of invention and improvement in Europe seems to be absolutely taking a nap. We have nothing to communicate to you but of the small kind, such as making the axletree turn with the wheel, which has been proposed here, adopted by some, and thought to be proved best by experiment, though theory has nothing to urge in its favor. A hydrostatic waistcoat is lately announced, which a person puts on either above or below his clothes in a minute, and fills with air by blowing with the mouth in twelve seconds. It is not yet shown, however, so I cannot tell you either the manner or matter of its construction. It may be useful when the loss of a vessel is foreseen. Herschell's discovery of two satellites to his planet, you have heard of ere this. He first saw them in January last. One revolves round its principal in about a week; the other in about a fortnight. I think your conjecture that the periodical variation of light in certain fixed stars proceeds from Maculæ, is more probable than that of Maupertius, who supposes those bodies may be flat, and more probable also than that which supposes the star to have an orbit of revolution so large as to vary sensibly its degree of light. The latter is rendered more difficult of belief from the shortness of the period of variation. I thank you for the shells you sent me. Their identity with marine shells and their vicinity to the sea, argue an identity of cause. But still the shells found in the mountains are very imperfectly accounted for. I have lately become acquainted with a memoire on a petrification mixed with shells by a Monsieur de La Sauvagere, giving an exact account of what Voltaire had erroneously stated in his questions Encyclopediques, article Coquilles, from whence I had transferred it into my notes. Having been lately at Tours, I had an opportunity of enquiring into de La Sauvagere's character, and the facts he states. The result was entirely in his and their favor. This fact is so curious, so circumstantially detailed, and yet so little like any known operation of nature, that it throws the mind under absolute suspense. The memoir is out of print. But my bookseller is now in search of it, and if he can find it I will put a copy of it into a box of books I shall send by the September packet, addressed to Mr. Wythe. In the same box I will put for you the Bibliotheque Physico-economique, for 1786, 1787, the connoissance des tems, Fourcroy's Chemistry, wherein all the later discoveries are digested, and a number of my notes on Virginia, of a copy of which you will be pleased to accept. It is a poor crayon, which yourself and the gentlemen which issue from your school must fill up. We are doubtful here whether we are to have peace or war. The movements