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sought to concentrate the rays by means of a quartz lens. The experiment is unattended with difficulty. An image of the anticathode is obtained, extremely well-defined as to size and distance by a heightened glow of the small spark.

The existence of refraction rendered that of regular reflection extremely probable; as a matter of fact, regular reflection does take place. By means of a quartz lens, or a lens formed by a very thin horn envelope filled with turpentine, I produce a conjugate focus of the anticathode; then I intercept the emerging pencil by a sheet of polished glass, placed obliquely ; I then obtain a focus exactly symmetrical, in respect to the plane of reflection, with the one which existed before the glass was interposed. With a plate of ground glass there is no regular reflection, but diffusion is observed.

If one half of a lamina of mica is roughened, the polished half lets pass the radiations, and the other half stops them (note 3).

This allows of the repetition of the refraction experiments under much more precise 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 no longer produces any fluorescence, and is itself absolutely invisible in the dark. They are fainter, however, in this case. They can also be produced continuously by means of an electric machine giving a spark a few millimetres in length.

At first I had attributed to Röntgen rays the polarization which in reality belongs to the new rays, a confusion which it was impossible to avoid before having observed the refraction, and it was only after making this observation that I could with certainty conclude that I was not dealing with Röntgen rays, but with a new species of light.

It is interesting to collate these remarks with the view expressed by M. Henri Becquerel, that in certain of his experiments “manifestations identical with those giving refraction and total reflection of light may have been produced by luminous rays which had traversed aluminium” (see Comptes Rendus, t. xxxii., March 25, 1901, p. 739).

On the Existence, in the Rays emitted by an

Auer Burner, of Radiations which traverse metals, wood, etc. (May 11, 1903).

A focus tube emits, as I have already proved (see p. 7), certain radiations susceptible of traversing metals, black paper, wood, etc. Amongst these, there are some for which the index of refraction of quartz is nearly 2. On the other hand, the index of quartz for the rays remaining from rocksalt, discovered by Professor Rubens, is 2:18. This similarity of indices led me to think that the radiations observed in the emission of a focus tube would very likely be near neighbours of the rays discovered by Rubens, and that consequently, they would be met with in the radiation emitted by an Auer burner, which is the source of such rays. I accordingly made the following experiment: an Auer burner is enclosed in a kind of lantern of sheet-iron, completely enclosed on all sides, with the exception of openings for the passage of air and combustion

gases, which are so arranged that no light escapes; a rectangular orifice, 4 cms. wide and 6.5 cms. high, cut in the iron at the same height as the incandescent mantle, is closed by a sheet of aluminium i mm. thick. The chimney of the Auer burner is of sheet-iron, and a slit 2 mms. wide and 3'5 cms. high is cut in it, opposite the mantle, so that the emerging luminous pencil is directed on the aluminium sheet. Outside the lantern, and in front of this sheet, a double-convex quartz lens is placed, having 12 cms. focal length for yellow light, behind which is a spark-gap of the kind already described, giving very small sparks. The spark is produced by a small induction-coil, provided with a rotating make and break device, which works with perfect regularity.

The distance p of the lens from the slit being 26.5 cms., one notes, by help of the spark, the existence of a focus of very great sharpness at a distance, p', of about 13.9 cms. For at this point the spark exhibits a notably greater glow than at the neighbouring points, whether in front or behind, above or below, to the right or to the left. The distance of this focus from the lens can be

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