Gem #3: Newton's Principia

Isaac Newton is arguably one of the greatest scientists (and mathematicians) of all times, and his Principia is one of the great works from the history of mathematics. Together with Leibniz, Newton is normally acknowledged as the founder of differential and integral calculus. If you want to download Principia to your computer, you can head over to the Internet Archive. The original was in Latin, but you can read an English translation below:

Newton's Principia