Beyond a doubt truth bears the same relation to falsehood as light to darkness.

I am never weary of being useful... In serving others I cannot do enough. No labor is sufficient to tire me.

Therefore, O students, study mathematics and do not build without foundations.

If a man has a tent made of linen of which the apertures have all been stopped up, and be it twelve bracchia across (over twenty-five feet) and twelve in depth, he will be able to throw himself down from any height without sustaining injury. [His concept of the parachute.]

I have been impressed with the urgency of doing. Knowing is not enough; we must apply. Being willing is not enough; we must do.

Just as courage imperils life, fear protects it.

Just as courage is the danger of life, so is fear its safeguard.