The information given by me to the Marquis de Chastellux, and alluded to in his book and in your letter was, that the sea breezes which prevail in the lower parts of Virginia during the summer months, and in the warm parts of day, had made a sensible progress into the interior country: that formerly, within the memory of persons living, they extended but little above Williamsburg; that afterwards they became sensible as high as Richmond; and that, at present, they penetrate sometimes as far as the first mountains, which are above an hundred miles further from the sea coast than Williamsburg is. It is very rare, indeed, that they reach those mountains, and not till the afternoon is considerably advanced. A light north-westerly breeze is, for the most part, felt there, while an easterly or north-easterly wind is blowing strongly in the lower country. How far northward and southward of Virginia this easterly breeze takes place, I am not informed. I must, therefore, be understood as speaking of that State only, which extends on the sea coast from 36½ to 38 of latitude. This is the fact. We know too little of the operations of nature in the physical world to assign causes with any degree of confidence. Willing always, however, to guess at what we do not know, I have sometimes indulged myself with conjectures on the causes of the phenomena above stated. I will hazard them on paper for your amusement, premising for their foundation some principles believed to be true. Air resting on a heated and reflecting surface, becomes warmer, rarer and lighter? it ascends therefore, and the circumjacent air, which is colder and heavier, flows into its place, becomes warmed and, lightened in its turn, ascends, and is succeeded as that which went before. If the heated surface be circular, the air flows to it from every quarter, like the rays of a circle to its centre. If it be a zone of determinate breadth and indefinite length, the air will flow from each side perpendicularly on it. If the currents of air flowing from opposite sides, be of equal force, they will meet in equilibrio, at a line drawn longitudinally through the middle of the zone. If one current be stronger than the other, the stronger one will force back the line of equilibrium towards the further edge of the zone, or even beyond it: the motion it has acquired causing it to overshoot the zone, as the motion acquired by a pendulum in its descent causes it to vibrate beyond the point of its lowest descent.