It ought further to be mentioned that Euler saw that the inner nature of gravitation must ultimately be referred to an "inclination and desire" (thus will) peculiar to material bodies (in the 68th letter to the Princess).
Oraindik ohartzea merezi du Eulerrek jadanik ulertu zuela grabitazioaren esentzia azken finean gorputzen (beraz nahimen) batera murriztu behar zela.