Preparation for reading Principia

These Directions from Mr Newton by his own hand were given to Richard Bentley in the summer of 1691.

Next after Euclid's Elements the Elements of y^e Conic sections are to be understood. And for this end you may read either the first part of y^e Elementa Curvarum of John De Witt, or De la Hire's late treatise of y^e conick sections, or Dr Barrow's epitome of Apollonius.

For Algebra read first Barthin's introduction & then peruse such Problems as you will find scattered up & down in y^e Commentaries on Cartes's Geometry & other Alegraical writings of Francis Schooten. I do not mean y^t you should read over all those Commentaries, but only y^e solutions of such Problems as you will here & there meet with. You may meet with De Witt's Elemenla curvarum & Bartholin's introduction bound up together w^th Carte's Geometry & Schooten's commentaries.

For Astronomy read first y^e short account of y^e Copernican System in the end of Gassendus's Astronomy & then so much of Mercator's Astronomy as concerns y^e same system & the new discoveries made in the heavens by Telescopes in the Appendix.

These are sufficient for understanding my book: but if you can procure Hugenius's Horologium oscillatorium, the perusal of that will make you much more ready.

At y^e first perusal of my Book it's enough if you understand y^e Propositions wth some of y^e Demonstrations w^ch are easier then the rest. For when you understand y^e easier they will afterwards give you light into y^e harder. When you have read y^e first 60 pages, pass on to y^e 3^d Book & when you see the design of that you may turn back to such Propositions as you shall have a desire to know, or peruse the whole in order if you think fit.