On the relative motion of the earth and the luminiferous æther

by Albert A. Michelson; Edward Williams Morley

. If now the velocity of the mirrors be increased sufficiently, their phases still being exactly the same, both images will be deflected from

and

, in inverse proportion to the velocities of light in the two directions; or, if the two deflections are made equal, and the difference of phase of the mirrors be simultaneously measured, this will evidently be proportional to the difference of velocity in the two directions. The only real difficulty lies in this measurement. The following is perhaps a possible solution.

(fig. 4 ([Figure 07])) are two gratings on which sunlight is concentrated. These are placed so that after falling on the revolving mirrors

and