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Rh produces any. A piece of sheet-iron or silver, heated to dull redness by a Bunsen burner, placed behind them, gives off rays at about the same rate as an Auer burner.

A plate of polished silver was arranged so that its plane made an angle of 45° with the horizontal plane. This plate having been heated to cherry-red by a Bunsen burner, its upper face emitted rays analogous to those of an Auer burner. A horizontal pencil of these rays, after traversing two sheets of aluminium of 0.3 mm. total thickness, sheets of black paper, etc., was concentrated by a quartz lens; with the aid of the small spark, the existence of four focal regions was ascertained. I further found that the action on the spark was much more pronounced when the spark was arranged vertically — that is, in the plane of emission — than when it was normal to this plane. The new radiations emitted by the polished plate are therefore polarized, as are the light and heat emitted at the same time. The silver plate having been covered with lampblack, the intensity of emission increased, but the polarization disappeared.