I can never satisfy myself until I can make a mechanical model of a thing. If I can make a mechanical model, I can understand it. As long as I cannot make a mechanical model all the way through I cannot understand.

You know only insofar as you can measure.

If you study science deep enough and long enough, it will force you to believe in God.

We all confidently believe that there are at present, and have been from time immemorial, many worlds of life besides our own. . . . [This] may seem wild, and visionary; all I maintain is that it is not unscientific.

If we can't express what we know in the form of numbers, we really don't know much about it.

I have no satisfaction in formulas unless I feel their numerical magnitude.

Heavier-than-air flying machines are impossible.