392 Mr. A. A. Campbell Swinton on the Circulation of 



found to be more and more distinctly the case the higher the 

 exhaustion. 



It seems therefore that at high vacua at any rate some 

 portion of the positive electricity passing through the tube is 

 carried by the positively charged atoms or particles that form 

 the anode-stream. Very probably at lower exhaustions the 

 electric discharge passes through the tube chiefly by an inter- 

 change of electrical charges from molecule to molecule on the 

 Grrothuss chain principle. At very high exhaustions, however, 

 when the mean free path becomes considerable, this may cease 

 to be the case, at any rate to a large degree ; and there may 

 be to some extent a regular and complete circulation of the 

 positively and negatively charged atoms, some of which may 

 make the entire journey from anode to cathode, or vice versa, 

 and deliver up their charges not by interchange with other 

 gaseous atoms, but by direct convexion to the electrodes of 

 opposite sign. 



Fig. 3. 



It may be mentioned that for showing the movements of 

 the streams a tube of the form illustrated in fig. 1 is not 

 essential, the anode-stream being equally well marked in a 

 tube of the ordinary globular form, provided the wheel is 

 mounted so as to be half contained within a glass cup arranged 

 so as to prevent the stream acting equally and oppositely upon 

 the vanes upon diametrically opposite sides of the wheel, as 

 shown in fig. 3. Further, it is not necessary to employ the 

 sliding adjustment for the wheel, as the effects can be shown 

 equally well by moans of two separate tubes, one with its 



