A superstition is a premature explanation that overstays its time.

Doubt is the beginning, not the end, of wisdom.

Boundaries which mark off one field of science from another are purely artificial, are set up only for temporary convenience. Let chemists and physicists dig deep enough, and they reach common ground.

Let truth be a banner big enough to hide the man who holds it up.

When we try to imagine a chaos we fail. ... In its very fiber the mind is an order and refuses to build a chaos.

They will listen with both ears to what is said by the men just a step or two ahead of them, who stand nearest to them, and within arm's reach. A guide ceases to be of any use when he strides so far ahead as to be hidden by the curvature of the earth.

Nothing cools so fast as undue enthusiasm. Water that has boiled freezes sooner than any other.