PART III.--CONTINUED. LETTERS WRITTEN AFTER HIS RETURN TO THE U. S. DOWN TO THE TIME OF HIS DEATH. 1790-1826. TO DR. RUSH. POPLAR FOREST, August 17, 1811. DEAR SIR,--I write to you from a place ninety miles from Monticello, near the New London of this State, which I visit three or four times a year, and stay from a fortnight to a month at a time. I have fixed myself comfortably, keep some books here, bring others occasionally, am in the solitude of a hermit, and quite at leisure to attend to my absent friends. I note this to show that I am not in a situation to examine the dates of our letters, whether I have overgone the annual period of asking how you do? I know that within that time I have received one or more letters from you, accompanied by a volume of your introductory lectures, for which accept my thanks. I have read them with pleasure and edification, for I acknowledge facts in medicine as far as they go, distrusting only their extension by theory. Having to conduct my grandson through his course of mathematics, I have resumed that study with great avidity. It was ever my favorite one. We have no theories there, no uncertainties remain on the mind; all is demonstration and satisfaction. I have forgotten much, and recover it with more difficulty than when in the vigor of my mind I originally acquired it. It is wonderful to me that old men should not be sensible that their minds keep pace with their bodies in the progress of decay. Our old revolutionary friend Clinton, for example, who was a hero, but never a man of mind, is wonderfully jealous on this head. He tells eternally the stories of his younger days to prove his memory, as if memory and reason were the same faculty. Nothing betrays imbecility so much as the being insensible of it. Had not a conviction of the danger to which an unlimited occupation of the executive chair would expose the republican constitution of our government, made it conscientiously a duty to retire when I did, the fear of becoming a dotard and of being insensible of it, would of itself have resisted all solicitations to remain. I have had a long attack of rheumatism, without fever and without pain while I keep myself still. A total prostration of the muscles of the back, hips and thighs, deprived me of the power of walking, and leaves it still in a very impaired state. A pain when I walk, seems to have fixed itself in the hip, and to threaten permanence. I take moderate rides, without much fatigue; but my journey to this place, in a hard-going gig, gave me great sufferings which I expect will be renewed on my return as soon as I am able. The loss of the power of taking exercise would be a sore affliction to me. It has been the delight of my retirement to be in constant bodily activity, looking after my affairs. It was never damped as the pleasures of reading are, by the question of _cui bono?_ for what object? I hope your health of body continues firm.