In yours of May 14th, you acquaint me with your indisposition, which gave me great concern. The resolution you have taken to use more exercise is extremely proper, and I hope you will steadily perform it. It is of the greatest importance to prevent diseases; since the cure of them by physic is so very precarious. In considering the different kinds of exercise, I have thought that the quantum of each is to be judged of, not by time or by distance, but by the degree of warmth it produces in the body: Thus when I observe if I am cold when I get into a carriage in a morning, I may ride all day without being warmed by it, that if on horse back my feet are cold, I may ride some hours before they become warm; but if I am ever so cold on foot, I cannot walk an hour briskly, without glowing from head to foot by the quickened circulation; I have been ready to say, (using round numbers without regard to exactness, but merely to mark a great difference) that there is more exercise in one mile’s riding on horseback, than in five in a coach; and more in one mile’s walking on foot, than in five on horseback; to which I may add, that there is more in walking one mile up and down stairs, than in five on a level floor. The two latter exercises may be had within doors, when the weather discourages going abroad; and the last may be had when one is pinched for time, as containing a great quantity of exercise in a handful of minutes. The dumb bell is another exercise of the latter compendious kind; by the use of it I have in forty swings quickened my pulse from 60 to 100 beats in a minute, counted by a second watch: And I suppose the warmth generally increases with quickness of pulse.