**A** **volume** **entitled** **Opera** **posthuma** (**Leiden**, 1703) **contained** **his** "**Dioptrica**," **in** **which** **the** **ratio** **between** **the** **respective** **focal** **lengths** **of** **object-glass** **and** **eye-glass** **is** **given** **as** **the** **measure** **of** **magnifying** **power**, **together** **with** **the** **shorter** **essays** **De** **vitris** **figurandis**, **De** **corona** **et** **parheliis**, &**c**. **An** **early** **tract** **De** **ratiociniis** **tin** **ludo** **aleae**, **printed** **in** 16J7 **with** **Schooten'****s** **Exercitationes** **mathematicae**, **is** **notable** **as** **one** **of** **the** **first** **formal** **treatises** **on** **the** **theory** **of** **probabilities**; **nor** **should** **his** **investigations** **of** **the** **properties** **of** **the** **cissoid**, **logarithmic** **and** **catenary** **curves** **be** **left** **unnoticed**.

- **By** **consulting** **an** **account** **of** **my** **expenses** **at** **Cambridge**, **in** **the** **years** 1663 **and** 1664, **I** **find** **that** **in** **the** **year** 1664 **a** **little** **before** **Christmas**, **I**, **being** **then** **Senior** **Sophister**, **bought** **Schooten'****s** **Miscellanies** **and** **Cartes**' **Geometry** (**having** **read** **this** **Geometry** **and** **Oughtred'****s** **Clavis** **clean** **over** **half** **a** **year** **before**), **and** **borrowed** **Wallis'****s** **works**, **and** **by** **consequence** **made** **these** **annotations** **out** **of** **Schooten** **and** **Wallis**, **in** **winter** **between** **the** **years** 1664 **and** 1665.