Thus, given that the sines of the angles of incidence of different rays express the different forces whose total force (which causes the deviation and which is but the excess of the centrifugal force of the vortexes in the air over those in the glass, a force that always remains the same and is expressed by the perpendicular, is applied to these rays and presses them, it follows that since the deviations of these rays must stand to each other as the forces causing them, the sines of the angles of refraction of the different rays must necessarily stand in the same ratio to the sines of their angles of incidence,.e., ::