184 Mr Almy, On a Diminution of the Potential 



Table I. Magnet perpendicular to tube. 



Spark gap 

 (without 





















magnet) . . . 



11-5 



11-4 



11-5 



11 



11-2 



11-3 



11-5 



11-5 



11-5 



Spark gap 

 (with 





















magnet) . . . 



11-5 



9 



8 



7 



4 



3 



2 



2 



1-9 



Potential- 





















diff. 



104 



84 



76 



68 



42 



33 



25 



25 



24-5 



Diminution 





















in P.-D.... 







16 



24 



34 



62 



69 



80 



80 



80-5 



Magnetic 





















field in- 





















■ tensity ... 







40 



48 



54 



62 



69 



75 



120 



420 



Table II. Magnet parallel to tube. 



Spark gap (with- 

 out magnet)... 









12-5 







- 



Spark gap (with 

 magnet) 



12-5 



10 



7 



5 



3 



2 



1-7 



Potential-diff. . . . 



110 



90 



68 



51 



33 



25 



21 



Diminution of 

















P.-D 







20 



42 



59 



77 



85 



88 



Intensity of 

 magnetic field... 







180 



216 



290 



300 



312 



420 



The magnetic intensities given are those at the centre of 

 the cathode ; spark gaps in millimetres, potential differences in 

 static (cg.s.) units, according to Heydweiller (cf. Wied. Ann. Vol. 

 48, p. 214). 



That the same sort of effect is produced with continuous 

 discharge was shown by using a large Holtz machine to give the 

 discharge. Potential differences were measured with a Kelvin 

 absolute electrometer; gas pressure being about 011 mm. 



That the relatively large change in potential difference is 

 only produced at fairly small gas pressures became veiy soon 

 evident. A series of observations of the diminution produced 

 by a certain magnetic field, normal to the tube, of intensity large 

 enough to be safely above the " critical " intensity, with various 



