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Rh been extinguished and removed the phosphorescent glow, to my great surprise, remained almost as strong as ever, but was darkened by the interposition of lead, or wet paper, or the hand, between the lantern and the sulphide. Nothing was altered by the suppression of the Auer burner, except that the observed actions grew progressively weaker. At the end of twenty minutes they still existed, but were scarcely noticeable.

Studying closely the circumstances of the phenomenon, I was not long in recognizing that the quartz lens had itself become a source of "N" rays; for when this was removed, all action on the sulphide ceased, whereas if it was brought nearer the sulphide, even laterally, the latter would become more luminous. I then took a quartz plate 15 mms. thick, whose surface formed a square of 5-cm. sides, and exposed this to the "N" rays emitted by an Auer burner through two sheets of aluminium and some black paper. It became as active as the lens; when brought nearer the sulphide, it seemed, according to Bichat's expression, as if a veil darkening it was being removed. A still more