Do not think of knocking out another person's brains because he differs in opinion from you. It would be as rational to knock yourself on the head because you differ from yourself ten years ago.

Ignorance breeds monsters to fill up the vacancies of the soul that are unoccupied by the verities of knowledge.

Knowledge has its boundary line, where it abuts on ignorance; on the outside of that boundary line are ignorance and miracles; on the inside of it are science and no miracles.

Knowledge is a mimic creation.

Knowledge is but an instrument, which the profligate and the flagitious may use as well as the brave and the just.

If there is anything for which I would go back to childhood, and live this weary life over again, it is for the burning, exalting, transporting thrill and ecstasy with which the young faculties hold their earliest communion with knowledge.