Archimedes, that he might transport the entire globe ... demanded only a point that was firm and immovable; so also, I shall be entitled to entertain the highest expectations, if I am fortunate enough to discover only one thing that is certain and indubitable.

Neither divine grace nor natural knowledge ever diminishes freedom.

For to be possessed of a vigorous mind is not enough; the prime requisite is rightly to apply it.

I should consider that I know nothing about physics if I were able to explain only how things might be, and were unable to demonstrate that they could not be otherwise.

The rainbow is such a remarkable phenomenon of nature, and its cause has been so meticulously sought after by inquiring minds throughout the ages, that I could not choose a more appropriate subject for demonstrating how, with the method I am using, we can arrive at knowledge not possessed at all by those whose writings are available to us.

In order to improve the mind, we ought less to learn, than to contemplate.

Except our own thoughts, there is nothing absolutely in our power.