You don't get into trouble because of the things you don't know. It is the things you don't know you don't know that really get you into a mess.

Nature never breaks her own laws.

A well-spent day brings happy sleep.

A bird is an instrument working according to mathematical law, which instrument it is within the capacity of man to reproduce with all its movements.

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

O speculators about perpetual motion, how many vain chimeras have you created in the like quest? Go and take your place with the seekers after gold.

Simplicity is the ultimate sophistication.