When your friends begin to flatter you on how young you look, it's a sure sign you're getting old.

I have deeply regretted that I did not proceed far enough at least to understand something of the great leading principles of mathematics, for men thus endowed seem to have an extra sense.

Do not worry about your difficulties in Mathematics. I can assure you, mine are still greater.

Don't interrupt me while I'm interrupting.

My most brilliant achievement was my ability to be able to persuade my wife to marry me.

"I hope, sir, that I will shoot your picture on your hundredth birthday." I don't see why not, young man. You look reasonably fit and healthy.