DEAR SIR,--I take shame to myself for having so long left unanswered your valuable favor on the subject of the mountains. But in truth, I am become lazy as to everything except agriculture. The preparations for harvest, and the length of the harvest itself, which is not yet finished, would have excused the delay however, at all times and under all dispositions. I examined, with great satisfaction, your barometrical estimate of the heights of our mountains; and with the more, as they corroborated conjectures on this subject which I had made before. My estimates had made them a little higher than yours (I speak of the Blue Ridge). Measuring with a very nice instrument the angle subtended vertically by the highest mountain of the Blue Ridge opposite to my own house, a distance of about eighteen miles south westward, I made the highest about two thousand feet, as well as I remember, for I can no longer find the notes I made. You make the south side of the mountain near Rockfish Gap, one thousand seven hundred and twenty-two feet above Woods'. You make the other side of the mountain seven hundred and sixty-seven feet. Mr. Thomas Lewis deceased, an accurate man, with a good quadrant, made the north side of the highest mountain opposite my house something more (I think) than one thousand feet; but the mountain estimated by him and myself is probably higher than that next Rockfish Gap. I do not remember from what principles I estimated the Peaks of Otter at four thousand feet; but some late observations of Judge Tucker's coincided very nearly with my estimate. Your measures confirm another opinion of mine, that the Blue Ridge, on its south side, is the highest ridge in our country compared with its base. I think your observations on these mountains well worthy of being published, and hope you will not scruple to let them be communicated to the world. You wish me to present to the Philosophical Society the result of my philosophical researches since my retirement. But, my good Sir, I have made researches into nothing but what is connected with agriculture. In this way, I have a little matter to communicate, and will do it ere long. It is the form of a mould-board _of least resistance_. I had some years ago conceived the principles of it, and I explained them to Mr. Rittenhouse. I have since reduced the thing to practice, and have reason to believe the theory fully confirmed. I only wish for one of those instruments used in England for measuring the force exerted in the draughts of different ploughs, &c., that I might compare the resistance of my mould-board with that of others. But these instruments are not to be had here. In a letter of this date to Mr. Rittenhouse, I mention a discovery in animal history, very signal indeed, of which I shall lay before the Society the best account I can, as soon as I shall have received some other materials collecting for me.