If a belief is not realized immediately in open deeds, it is stored up for the guidance of the future.

No simplicity of mind, no obscurity of station, can escape the universal duty of questioning all that we believe.

We may always depend on it that algebra, which cannot be translated into good English and sound common sense, is bad algebra.

Thought is powerless, except it make something outside of itself: the thought which conquers the world is not contemplative but active.

Remember that [scientific thought] is the guide of action; that the truth which it arrives at is not that which we can ideally contemplate without error, but that which we may act upon without fear; and you cannot fail to see that scientific thought is not an accompaniment or condition of human progress, but human progress itself.

An atom must be at least as complex as a grand piano.

If a man, holding a belief which he was taught in childhood or persuaded of afterwards, keeps down and pushes away any doubts which arise about it in his mind, purposely avoids the reading of books and the company of men that call in question or discuss it, and regards as impious those questions which cannot easily be asked without disturbing it - the life of that man is one long sin against mankind.