"I confess that I have never found in my experience that anything which I once clearly understood could afterwards be called into doubt by me."

"Travelling is almost like talking with those of other centuries."

"The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge."

"It is a mark of a truly great mind to be able to make a great discovery with few means."

"I was very surprised to find that I had been mistaken more often than not in my life."