No great discovery was ever made without a bold guess.

If I have ever made any valuable discoveries, it has been owning more to patient attention, than to any other talent.

There is one thing stronger than all the armies in the world; and that is an idea whose time has come.

To every action there is always opposed an equal reaction: or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.

Tact is the knack of making a point without making an enemy.

I frame no hypotheses; for whatever is not deduced from the phenomena is to be called an hypothesis; and hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy.

Plato is my friend; Aristotle is my friend, but my greatest friend is truth.

A man may imagine things that are false, but he can only understand things that are true.

The change in motion is proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed.