Diagram, by John Collins Figures in a letter to Henry Oldenburg from John Collins, who had been editing the works on curves and conic sections by John Wallis and Isaac Barrow. Diagram shows a triangle with lines and curves inside it, and a semi-circle with lines and triangles inside it, both with various measurements and angles labelled within them. Collins proposed several problems relating to these works to Renatus Franciscus Slusius via this letter. Subject: Mathematics c.15 March 1670