...if I shall have sufficient strength to improve and amplify what was written and published by me up to now about motion by adding some little speculations, and in particular those relating to the force of percussion, in the investigation of which I have consumed hundreds and thousands of hours, and finally reduced this to very easy explanation, so that people can understand it in less than half an hour of time.

It now remains that we find the amount of time of descent through the channel. This we shall obtain from the marvelous property of the pendulum, which is that …

I have been in my bed for five weeks, oppressed with weakness and other infirmities from which my age, seventy four years, permits me not to hope release. Adde…

I tell you that if natural bodies have it from Nature to be moved by any movement, this can only be circular motion, nor is it possible that Nature has given t…

And so I penned It down, until at last it came to be, For length and breadth, the bigness which you see.

Every book has an intrinsic impossibility, which its writer discovers as soon as his first excitement dwindles.

The real geniuses know where their writing has to be good and where they can get away with some mediocrity.