Modification of an air pump

A sketch of a 'pneumatic engine' (air pump) designed by Christian Huygens, with lettering to indicate its parts.

This is most likely the enlarged copy from the original letter from Huygens (EL/H1/18) to Robert Moray dated 2 February 1663 [New Style}, which was ordered with a translation (EL/H1/19) at the meeting of the Royal Society on 28 January 1663 [Old Style]. The paper was read the following week, 4 February 1663.