Isaac Newton’s Mathematica Principia (1687) has been described as the most important, but also the least read, scientific book ever written. It has been little read mostly because it has been little comprehended. The book is filled with complex geometric diagrams, and Newton’s explanations are brief, the assumption being that the reader’s mathematical knowledge and ability is very high.
However, there is at least one result that Newton derived in the Principia that is fairly easy to understand, and I will describe it in this post. It also happens to be one of the important theorems in the Principia: a proof that Kepler’s Second Law of planetary motion isa consequence of mechanics.

This post is about creating, displaying, and publishing documents that have mathematical content. This is a troublesome thing for mathematics and science workers, because most word processing systems treat math as an add-on or an afterthought, if they have any provision for it at all. Even when mathematics is supported, it may be difficult or impossible to do much more than print the document on paper.