Knowledge keeps no better than fish.

One main factor in the upward trend of animal life has been the power of wandering.

The factor in human life provocative of a noble discontent is the gradual emergence of a sense of criticism, founded upon appreciation of beauty, and of intellectual distinction, and of duty.

It is the business of the future to be dangerous; and it is among the merits of science that it equips the future for its duties.

What the learned world tends to offer is one second-hand scrap of information illustrating ideas derived from another second-hand scrap of information. The second-handedness of the learned world is the secret of its mediocrity.

Heaven knows what seeming nonsense may not tomorrow be demonstrated truth.

The difference between ancients and moderns is that the ancients asked what have we experienced, and moderns asked what can we experience.