conditions, by the use of Newton's arrangement for obtaining a pure spectrum.
From all that precedes, the fact results that the rays which I have thus studied are not Röntgen rays, since these undergo neither refraction nor reflection. In fact, the little spark reveals a new species of radiations emitted by the focus tube, which traverse aluminium, black paper, wood, etc. These are plane-polarized from the moment of their emission, are susceptible of rotatory and elliptic polarization, are refracted, reflected, diffused, but produce neither fluorescence nor photographic action.
I had expected to find that amongst these rays some existed whose refractive index for quartz is about 2; but probably quite a spectrum of such rays exists, for in the refraction experiments with a prism, the deviated pencil appears to cover a broad angle. The study of this dispersion remains to be pursued, as well as that of the wave-lengths of the rays.
By progressively diminishing the intensity of the current actuating the induction-coil, one still gets these new rays, even when the tube
