I am ashamed to tell you to how many figures I carried these calculations [of Pi], having no other business at the time

Pictures, propagated by motion along the fibers of the optic nerves in the brain, are the cause of vision.

Those qualities of bodies that cannot be intended and remitted [i.e., qualities that cannot be increased and diminished] and that belong to all bodies on which experiments can be made should be taken as qualities of all bodies universally.

All knowledge and understanding of the Universe was no more than playing with stones and shells on the seashore of the vast imponderable ocean of truth.

I do not feign hypotheses.

Trials are medicines which our gracious and wise Physician prescribes because we need them; and he proportions the frequency and weight of them to what the case requires. Let us trust his skill and thank him for his prescription.

Sir Isaac Newton was asked how he discovered the law of gravity. He replied, "By thinking about it all the time.