Paper of directions given by Newton to Bentley respecting the books to be read before endeavoring to read and understand the Principia

c. July 1691

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

For algebra read first Barthin’s introduction and then peruse such problems as you will find scattered up & down in the commentaries on Descartes’s Geometry and other algebraical writings of Francis Schooten. I do not mean that you should read over all those commentaries, but only the solutions of such problems as you will here & there meet with. You may meet with De Witt’s Elementa curvarum & Bartholin’s introduction bound up together with Descartes’s Geometry and Schooten’s commentaries.

For astronomy read first the short account of the Copernican system in the end of Gassendi’s Astronomy & then so much of Mercator’s Astronomy as concerns the 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 Huygens’s Horologium oscillatorium, the perusal of that will make you much more ready. …