Page:"N" Rays (Garcin).djvu/102

72 N$1$ rays can be stored up like "N" rays. For instance, one need only bring a bit of stretched copper wire in proximity to a lump of quartz to make the quartz emit N$1$ rays for some time after.

Consider a phosphorescent screen, or, more generally, a dimly lighted surface. If this surface is viewed normally, one notices that the action of "N" rays is to render it more luminous; if, on the contrary, the surface is viewed very obliquely, nearly tangentially, the action of "N" rays is to render it less luminous. In other words, the action of "N" rays increases the quantity of light normally emitted, while it diminishes the light emitted in a very oblique direction. If one looks at it in an intermediate position, no appreciable effect is observed. This explains the fact, observed