We scarce know to whom we are indebted for the compass, and spectacles, nor have even paper and printing, that record every thing else, been able to preserve with certainty the name and reputation of their inventors. One would not, therefore, of all faculties or qualities of the mind, wish, for a friend or a child, that he should have that of invention. (To @John @Lining, March 18, 1755)
ERROR. There are few, though convinced, that know how to give up, even an error, they have been once engaged in maintaining; there is therefore the more merit in dropping a contest where one thinks one's self right; 'tis at least respectful to those we converse with. And indeed all our knowledge is so imperfect, and we are from a thousand causes so perpetually subject to mistake and error, that positiveness can scarce ever become even the most knowing; and modesty in advancing any opinion, however plain and true we may suppose it, is always decent, and generally more likely to procure assent. (To @Mary @Stevenson, [1759])
EXERCISE. 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 horseback 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 sixty to one hundred beats in a minute, counted by a second watch; and I suppose the warmth generally increases with quickness of pulse. (To @William @Franklin, August 19, 1772)
MORAL ALGEBRA. When difficult cases occur, they are difficult, chiefly because while we have them under consideration, all the reasons pro and con are not present to the mind at the same time; but sometimes one set present themselves, and at other times another, the first being out of sight. Hence the various purposes or inclinations that alternately prevail, and the uncertainty that perplexes us.
To get over this, my way is, to divide half a sheet of paper by a line into two columns; writing over the one Pro, and over the other Con. Then during three or four days consideration, I put down under the different heads short hints of the different motives, that at different times occur to me, for or against the measure. When I have thus got them all together in one view, I endeavor to estimate their respective weights; and where I find two, one on each side, that seem equal, I strike them both out. If I find a reason pro equal to some two reasons con, I strike out the three. If I judge some two reasons con, equal to some three reasons pro, I strike out the five; and thus proceeding I find at length where the balance lies; and if after a day or two of farther consideration, nothing new that is of importance occurs on either side, I come to a determination accordingly.
