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Rh

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 rock-salt, 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