Positive Streams in “Crookes” Tubes

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REFERRING to the abstract of Mr. F. W. Aston's very interesting paper read before the Royal Society on December 13, 1906, “On Experiments on the Length of the Kathode Dark Space with Varying Current Densities and pressure in different Gases,” published in your issue for April 11 (p. 574), may I point out in reference to the therein contained statement that “the stream of positive ions may be strikingly shown by a rotatory mica mill mounted inside the dark space which rotates violently in the opposite direction to the familiar ones designed to show the motion of kathode rays away from the electrode,” that in my two papers “On the Circulation of the Residual Gaseous Matter in a Crookes' Tube,” read before the Physical Society, and published in the Philosophical Magazine for October, 1898, I showed similar results, i.e. that mica mill wheels which turned in one direction under kathode-ray bombardment, turned in the opposite direction when so placed as to be just outside of the stream of kathode rays, thus indicating a current of particles proceeding towards the kathode, which particles I found to be charged positively?

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