It is more fully explained by him, with later simplifications, in Principia mathematica (Cambridge).
mathematica, and Rhetorica, and Grammatica are also among the best known.
His writings on light, Perspectiva and Specula mathematica, are included in his Opus majus.
Speculativa is divided into naturalis (physics), mathematica, and divina (metaphysics).
The discussion in this book can be combined with his mathematica software, available on that site.