History of the Leray Projection

Question

I am hoping to cite the first use of the Leray projection, $\mathbb{P}$, onto the divergence-free vector-field.

I tried scanning Leray's famous 1934 paper, 'Sur le mouvement...,' but couldn't find it, and I don't know enough French to say with confidence that it's not in there somewhere.

Anyone know when the projection operator was first used and by whom?

Answer 1

A scan of the paper can be found here. In the original publication, it was not referred to as a projection, but it was used to write the pressure in terms of an application of the 3D Laplacian Green's function on the velocity. This was not used to write an abstract evolution equation in terms of just $u$ as is typical now, but it was used to derive many integral bounds on the weak form of the Navier-Stokes equation.