The scientific imagination always restrains itself within the limits of probability.

That which endures is not one or another association of living forms, but the process of which the cosmos is the product, and of which these are among the transitory expressions.

Education is the instruction of the intellect in the laws of Nature, under which name I include not merely things and their forces, but people and their ways; and the fashioning of the affections and of the will into an earnest and loving desire to move in harmony with those laws.

In the world of letters, learning and knowledge are one, and books are the source of both; whereas in science, as in life, learning and knowledge are distinct, and the study of things, and not of books, is the source of the latter.

Life is too short to occupy oneself with the slaying of the slain more than once.

I doubt the fact, to begin with, but if it be so even, what is this but in grand words asking me to believe a thing because I like it.

You may read any quantity of books, and you may almost as ignorant as you were at starting, if you don't have, at the back of yourminds, the change for words in definite images which can only be acquired through the operation of your observing faculties on the phenomena of nature.