He who does not understand the supreme certainty of mathematics is wallowing in confusion.

He who walks straight rarely falls.

Having wandered some distance among gloomy rocks, I came to the entrance of a great cavern ... Two contrary emotions arose in me: fear and desire--fear of the threatening dark cavern, desire to see whether there were any marvelous things in it.

I shall do down in history as the man who opened a door!

When the thing taken into union is perfectly adapted to that which receives it, the result is delight and pleasure and satisfaction.

If we make mistakes in our first compositions and do not know them, we may not amend them.

Iron rusts from disuse; water loses its purity from stagnation... even so does inaction sap the vigor of the mind.