The foregoing leads one to think that the emission of radiations susceptible of traversing metals, etc., is an extremely general phenomenon. First observed in the emission of a focus tube, it was also met in that of ordinary sources of light and heat. For shortness, I will henceforward designate these rays by the name of "N" rays.
I would draw attention to the fact that these "N" rays comprise a very large variety of radiations; for while those which issue from an Auer burner have refractive indices greater than 2, there are others, amongst those emitted by a Crookes' tube, whose index is inferior to 1.52, for if a pencil of these rays is made to impinge on an equilateral quartz prism, parallel to the edges and normal to one of the faces, an emerging pencil is obtained which is very much spread out.
Up to this time the only means of detecting the presence of "N" rays was by their
- From the name of the town of Nancy, these researches having been made at the Nancy University. In conformity with a usage which has become established, I now employ the letter "N" instead of "n," which I had at first adopted.