Diagram of a prism

The figure of a prism in Ignace-Gaston Pardies' criticism of Isaac Newton's 'experimentum crucis', in a letter of 3 April 1672, to Henry Oldenburg. These comments were passed on to Newton, who wrote a reply to these criticisms on 13 April 1672. The letter by Pardies and Newton's reply were read at the meeting of the Royal Society on 18 April 1672, and were printed in Philosophical Transactions vol. 7 no. 82 (June 1672).