It is not true that a man can believe or disbelieve what he will. But it is certain that an active desire to find any proposition true will unconsciously tend to that result by dismissing importunate suggestions which run counter to the belief, and welcoming those which favor it. The psychological law, that we only see what interests us, and only assimilate what is adapted to our condition, causes the mind to select its evidence.

Heart and Brain are the two lords of life. In the metaphors of ordinary speech and in the stricter language of science, we use these terms to indicate two central powers, from which all motives radiate, to which all influences converge.

Vehemence without feeling is but rant.

The discoverer and the poet are inventors; and they are so because their mental vision detects the unapparent, unsuspected facts, almost as vividly as ocular vision rests on the apparent and familiar.

No man ever made a great discovery without the exercise of the imagination.

Mathematicians do not write for the circulating library.

To one man a stream is so much water-power, to another a rendezvous for lovers.