Fundamental to any application of Cartesian philosophy in explaining the natural world were the laws of impact contained in Descartes's Principles of philosophy. Since action was restricted to collision, these laws governed all physical phenomena, and they became a focus for critical study of Descartes's mechanics.
When Huygens was staying in London in 1661, he was visited on 23 April by a group of English mathematicians – Moray, Brouncker, Paul Neile, Wallis, Rooke, Wren and Goddard – and he recorded in his journal, ‘Resolus les cas qu'ils me proposerent touchant les recontres de deux spheres’ (Huygens, 1888, vol. 22, p. 573). Prompted by Oldenburg in 1665, Moray recalled the occasion, ‘as both Dr. Wallis and I do well remember’. Huygens, apparently, had raised the subject of impact and since Wren and his colleague at Gresham College, Laurence Rooke, had already made some experiments – ‘with balls of wood & other stuff hanging by threads’ – they proposed a number of initial conditions to Huygens. Their host used his rules, which he did not reveal, to derive the results that Rooke and Wren had already achieved by experiment.
It was probably in 1661, though after the discussion with Huygens, that Wren evolved his own theory of elastic impact, a theory which came to light when the Royal Society took up the question in 1668. When the theories of Huygens and Wren were published in 1669, it was clear that they differed only in formulation.
We can date Wren's theory fairly closely.