the exception of a vertical slit cut at the same height as the Auer burner, and stopped up by transparent paper, a flame was disposed so as to light up the slit. By suitably placing the eye and the slit, the image of this latter is seen formed by reflection on the steel cylinder, and simultaneously the reflecting surface is receiving the "N" rays. It was then easy to observe that the action of these rays reinforces the image, for if they are intercepted, the image darkens, and turns to a reddish hue. I repeated this experiment with the same success by employing, instead of the knitting-needle, a plane mirror of bronze.
The same result is again obtained by reflecting the light on the polished face of a block of quartz. However, when the "N" rays fall normally on the refracting face, their action on reflected light disappears, whatever be the incidence of this light, whether it be that their action becomes zero, or simply inappreciable. In order that the light reflected by the quartz may be reinforced by the "N" rays, it is not necessary that the rays should be directed towards the interior of the quartz; the action
