Mathematics is the only true metaphysics.

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.

To measure is to know.

When you cannot measure, your knowledge is meager and unsatisfactory.

Vortices of pure energy can exist and, if my theories are right, can compose the bodily form of an intelligent species.

I have not the smallest molecule of faith in aerial navigation other than ballooning, or of the expectation of good results from any of the trials we heard of. So you will understand that I would not care to be a member of the Aeronautical Society.

In science there is only physics; all the rest is stamp collecting.