D_x = [epsilon]1 E_x, D_y = [epsilon]2 E_y, D_z = [epsilon]3 E_z, (14)

the constants [epsilon]1, [epsilon]2, [epsilon]3 (dielectric

constants) depending on the properties of the body considered. In an

isotropic medium they have a common value [epsilon], which is equal to

unity for the free aether, so that for this medium D = E.

(c) There is a relation similar to (14) between the magnetic force and

the magnetic induction. For the aether, however, and for all

ponderable bodies with which this article is concerned, we may write

B = H.

It follows from these principles that, in an isotropic dielectric,

transverse electric vibrations can be propagated with a velocity

v = c/[root][epsilon]. (15)