Mathematics should be mixed not only with physics but with ethics.

I put a piece of paper under my pillow, and when I could not sleep I wrote in the dark.

A man's wealth is measured by what he doesn't need.

Half the walk is but retracing our steps. We should go forth on the shortest walk, perchance, in the spirit of undying adventure, never to return-prepared to send beck our embalmed hearts only as relics to our desolate kingdoms. If you are ready to leave father and mother, brother and sister, and wife and child and friends and never see them again,-if you have paid your debts and made your will, and settled your affairs and are a free man, then you are ready for a walk.

When the first light dawned on the earth, and the birds awoke, and the brave river was heard rippling confidently seaward, and the nimble early rising wind rustled the oak leaves about our tent, all people, having reinforced their bodies and their souls with sleep, and cast aside doubt and fear, were invited to unattempted adventures.

The book exists for us, perchance, which will explain our miracles and reveal new ones.

It is difficult to begin without borrowing, but perhaps it is the most generous course thus to permit your fellowmen to have an interest in your enterprise.