Follow your genius closely enough, and it will not fail to show you a fresh prospect every hour.

A fortified town is like a man cased in the heavy armor of antiquity, with a horse-load of broadswords and small arms slung to him, endeavoring to go about his business.

He is not a true man of science who does not bring some sympathy to his studies, and expect to learn something by behavior as well as by application. It is childish to rest in the discovery of mere coincidences, or of partial and extraneous laws. The study of geometry is a petty and idle exercise of the mind, if it is applied to no larger system than the starry one. Mathematics should be mixed not only with physics but with ethics; that is mixed mathematics. The fact which interests us most is the life of the naturalist. The purest science is still biographical.

You must get your living by loving, or at least half your life is a failure.

Do not entertain doubts if they are not agreeable to you.

Oh, one world at a time!

Faint heart never won true friend. O my friend, may it come to pass, once, that when you are my friend I may be yours.