All of science can be divided into physics and stamp-collecting.
You know only insofar as you can measure.
When you are face to face with a difficulty, you are up against a discovery.
If you can not measure it, you can not improve it.
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.
I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind.