He seems to have shown signs of being unhappy with Descartes ' theory around this time but he still addressed the Académie on this topic in 1669 although after his address Roberval and Mariotte argued strongly, and correctly, against Descartes' theory and this may have influenced Huygens.
Siya tila sa may ipinapakita palatandaan ng pagiging malungkot sa Descartes' teorya sa paligid ng mga oras na ito ngunit siya pa rin ang direksiyon Académie sa paksang ito sa 1669 bagama't pagkatapos ng kanyang address Roberval at Mariotte argued Matindi, at tama, laban sa Descartes' teorya at ito ay maaaring may naiimpluwensyahan Huygens .