> We find first of all that it requires us to assume that gravitational propagation is not instantaneous, but occurs with the speed of light. One might think that this is reason enough to reject the hypothesis, since Laplace demonstrated that this cannot be the case.3 In reality, however, the effect of this propagation is compensated in large part by a different cause, in such a way that no contradiction arises between the proposed law and astronomical observations.

Paragraph 13 introduction 
[On the dynamics of the electron:
Introduction][1]


Laplace proved that the speed of gravity must be million times greater than speed of light, 

I couldn't find his proof, 

My question is how does he proved this to be true and how was it refuted?


  [1]: http://henripoincarepapers.univ-nantes.fr/chp/text/hp2007gg.html#bib.bib7