"The human mind is seldom satisfied, and is certainly never exercising its highest functions, when it is doing the work of a calculating machine."

"Thoroughly conscious ignorance is the prelude to every real advance in science."

"The mind of man is like a mirror, which reflects the images of things, but does not always reflect them truly."

"The velocity of light is a quantity of which we have now a more accurate knowledge than of any other physical constant."

"The only way of discovering the extent of the laws of nature is to try to transcend them."