Radio has no future." "X-rays are clearly a hoax". "The aeroplane is scientifically impossible.

Nothing can be more fatal to progress than a too confident reliance on mathematical symbols; for the student is only too apt to take the easier course, and consider the formula not the fact as the physical reality.

[Referring to Fourier's mathematical theory of the conduction of heat] ... Fourier's great mathematical poem.

[Of the ether] it is no greater mystery at all events than the shoemakers' wax.

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.

Questions of personal priority, however interesting they may be to the persons concerned, sink into insignificance in the prospect of any gain of deeper insight into the secrets of nature.

Simplification of modes of proof is not merely an indication of advance in our knowledge of a subject, but is also the surest guarantee of readiness for farther progress.