Mr Almy, On a Diminution of the Potential Difference, etc. 189 

 Table VI. Potential difference between the electrodes. 





Without 

 magnet 



Magnet 

 transverse 



Magnet 

 parallel 



With cathode a 



2200 

 5000 

 1600 

 4000 



1550 

 3900 

 1550 

 4000 



1500 

 3600 

 1550 

 4000 



With cathode b 



a surrounded with tinfoil 

 b surrounded with tinfoil 



Jfr 



c^ 



the effects produced have magnitudes in the ratio 6 : 10 while 

 the distance between the walls of the tube varies as 1 : 4. 



As this experiment is hardly to be re- 

 garded as conclusive a tube of the form 

 shown in Fig. 3 was tried. One electrode, 

 a thick aluminium wire, partly enclosed by 

 a thick-walled glass tube was inside the 

 other electrode, a cylinder, with end closed 

 by a disc of metal next the glass tube ; by 

 this form of electrodes the inner was shielded 

 from the action of a static charge on the 

 glass. 



With this tube the magnetic diminution 

 was produced, and, with the wire as cathode 

 the effect produced is of remarkable mag- 

 nitude, in some cases ; namely at times the 

 discharge reduces to a small luminous brush 

 or bundle of lines, passing from the wire to 

 the cylinder, resembling the arc discharge 

 at atmospheric pressure. (Table VII.) 



The potential differences in the two 

 cases indicated as < 400 was much smaller 

 than that necessary to give a single division 

 deflection of the voltmeter ; its actual mag- 

 nitude was not obtained. 



These results seem to show conclusively that the action of the 

 magnetic field is independent of any static charge on the walls of 

 the discharge-tube, since it is produced when the cathode is prac- 

 tically surrounded by the other electrode. 



In short, the action of the magnetic field seems to be simply 



Uju 



Fig. 3. 



