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.

Every particle of matter is attracted by or gravitates to every other particle of matter with a force inversely proportional to the squares of their distances.

My Design in this Book is not to explain the Properties of Light by Hypotheses, but to propose and prove them by Reason and Experiments: In order to which, I shall premise the following Definitions and Axioms.

I understood. I have understood. I do understand.

The great ocean of truth lay all undiscovered before me.

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

I keep the subject of my inquiry constantly before me, and wait till the first dawning opens gradually, by little and little, into a full and clear light.