The difficulty is not in the language that Newton uses, but in the incredibly original viewpoint that he takes. Get a good translation, by all means, but you'll also need the help of a good guide.

One of the best such guides I ever found was S. Chandrasekhar's fantastic "Newton's *Principia* for the Common Reader", Oxford University Press, 1995. (Don't be fooled by the title, though, apparently Chandrasekhar had a much higher opinion of the 'common reader' than is warranted by the available evidence.)

It doesn't cover the entire *Principia*, but mainly the parts that lead to Newton's results on gravity. What Chandrasekhar does is explain Newton's propositions, translate them into modern notation/language and show you a 'modern' proof, and then, with that knowledge of what is going on, he goes back to Newton's argument and shows the reader how Newton's approach works. Along the way, he comments on how Newton's ideas harked back to Euclid and, at the same time, anticipated concepts in mechanics that would not be developed until many years later.

It's an amazing, edifying work by one of the greatest astrophysicists of the 20th century.

shouldbe done, but only after you have the knowledge from the modern point of view. For historical perspective. Not in order tolearnfrom it. $\endgroup$ – Asaf Karagila Mar 29 '18 at 9:07