Nipher — Rotational Motion of Cathode Disc in Crookes Tube. 183 



answered. There is much reason to suspect that the gas par- 

 ticles do not shoot off normally from the surface of the disc, 

 but in a vortex, the axis of which is in the two dark spots 

 opposite the cathode faces. The fact that the anode does not 

 respond, and that similar experiments in open air have thus 

 far failed seems to point to the cathode discharge as the direct 

 active agent. This view is not easily reconciled with the 

 result of the experiment made by Crookes with the hemi- 

 cylindrical cathode (Nature, July 3, 1879, p. 229, Fig. 3), but 

 the figure shown does not seem to quite agree with the descrip- 

 tion of it. Experiments are now in preparation which will 

 decide this question. It is possible that the rotation observed 

 is a direct action and reaction between the current in the disc, 

 and the external field due to the current. In this case the 

 rotation apparently ought to be producible in open air, and 

 on the anode terminal of the Crookes tube. 



Whatever may be the direct agency producing this rotation, 

 it seems apparent that we now have an experimental basis for 

 imposing a term representing a rotation into the equations 

 representing the conditions within a conductor. 



Issued May 8,1896. 



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