5S 



Prof. J. A. Fleming on the 



remaining perfectly constant. It will then often suddenly 

 jump perhaps to 22 volts, and then slowly decrease to 19 volts, 

 or so. This tendency of the potential-difference between the 

 middle plate and positive lamp electrode to jump from a low 

 to a high value, or vice versa, is most marked in lamps in 

 which the plate is about half-way, and symmetrically placed, 

 between the legs of the carbon. We shall speak of these 

 two values as the high and low value of the current through 

 the galvanometer, and defer until later a discussion of some 

 other causes tending to make the current pass from a high to 

 a low value or the reverse, as well as its possible explanation. 

 In Table No. 2 are tabulated a set of observations on the same 

 lamp No. 4, showing these double values which the potential- 

 difference and current may have, and it may be here noted 

 that in the previous Table No. l,the higher values have been 

 taken in those cases in which double values exist. 



Table No. 2. Lamp No. 4. Milamperemeter. 



Table showing the multiple values of the potential-difference 

 between the middle plate and positive electrode of the 

 lamp corresponding to various given working voltages. 





Volts be- 



Current 





Volts be- 



Current 





tween the 



through the 





tween the 



through the 



Working 

 volts of 



middle plate 



graded gal- 



Working 



middle plate 



graded gal- 



and positive 



vanometer 



volts of the 



and positive 



vanometer 



the lamp. 



electrode of 



in milli- 



lamp. 



electrode of 



in milli- 





the lamp. 



amperes. 





the lamp. 



amperes. 



30 



•6 



•095 



39 



4-3 



•761 



32 



1-1 



•174 



;? 



140 



2-22 



34 



2-0 



•317 



40 



5-1 



•809 



35 



2-6 



•412 



?5 



18-1 



2-87 



36 



3-2 



•507 



41 



5-3 



•841 



37 



3-9 



•618 



ty 



18-4 



2-91 



38 



4-3 



•682 



42 



6-4 



1-01 



jj 



4-5 



•714 



)? 



20-0 



3-17 



jj 



11-0 



1-74 



43 



6-2 



•983 









V 



22-0 



3-49 



These observations are plotted in Curve No. 2, in which the 

 abscissae represent the working volts of the lamp and the 



