With God thoughts are colors, with us they are pigments-even the most abstract one may be accompanied by physical pain.

First there is a time when we believe everything, then for a little while we believe with discrimination, then we believe nothing whatever, and then we believe everything again - and, moreover, give reasons why we believe.

An hour-glass is a reminder not only of time's quick flight, but also of the dust to which we must at last return

Some theories are good for nothing except to be argued about.

If we thought more for ourselves we would have very many more bad books and very many more good ones.

The noble simplicity in the works of nature only too often originates in the noble shortsightedness of him who observes it.

Above all things expand the frontiers of science: without this the rest counts for nothing.