,
′ the corresponding velocities. From the above we easily deduce the relations
the latter of which gives the excess of density of the interior æther.
It is assumed that when the body is put in motion, only a part of the interior æther is carried along with it, and that this part is that which causes the excess in the density of the interior over that of the surrounding æther; so that the density of this moveable part is
. The other part which remains at rest during; the body's motion has the density
