ABSTRACT
Hitherto the focal lines of the concave mirrors were vertical, and the plane of oscillation was therefore perpendicular to the plane of incidence. The interferences that are produced in front of the mirror by the intersecting systems of waves and that give rise to characteristic phenomena in the circular conductor, are most likely to throw light on all problems relating to the change of phase and amplitude produced by reflection. The two concave mirrors were again placed side by side, as in the reflection experiment first described; but there was placed opposite them, as a reflecting surface, the screen of parallel copper wires that has already been referred to. The tourmaline plate absorbs the part that is not transmitted; our surface reflects it. If in the experiment last described the two mirrors are placed with their focal lines at right angles, no sparks can be excited in the secondary conductor by reflection from an isotropic screen.
