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10 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