74 



Prof. J. A. Fleming on the 



Table No. 9. Lamp No. 1. Milamperemeter. 



Table showing the potential-difference between the positive 

 electrode and the platinum wire, and the current flowing 

 through the galvanometer connecting them, for various 

 voltages of the lamp. 





Volts 

 between 



Milliampere 





Volts 

 between 



Milliampere 



Working 



volts of the 



lamp. 



platinum 

 wire and 

 positive 

 electrode. 



current 

 through the 

 galvano- 

 meter. 



Working 



volts of the 



lamp. 



platin um 

 wire and 

 positive 

 electrode. 



current 

 through the 

 galvano- 

 meter. 



80 



•1 



•016 



92 



1-7 



•270 



V 



•2 



•032 



>? 



2-4 



•381 



82 



•3 



•048 



93 



1-9 



•302 



83 



•2 



•032 



)* 



2-6 



•413 



84 



•4 



•064 



94 



32 



•509 



86 



•4 



•064 



5? 



9-4 



1-49 



5? 



•7 



•114 



95 



4-9 



•78 



87 



•5 



•080 ' 



96 



5-8 



•92 



88 



•8 



•127 



97 



7-1 



113 



v 



•9 



•142 



98 



8-3 



1-32 



90 



1-0 



•159 



99 



8-9 



1-41 



jj 



1-3 



•206 



100 



8-6 



1-37 



91 



1-4 



'222 



?> 



10-3 



1-64 



These figures show that at any definite working electro- 

 motive force of the lamp the current between the positive 

 electrode and the middle plate has very variable values, and 

 that it suddenly changes from one value to another without 

 any apparent reason, the working volts of the lamp remaining 

 constant all the time. 



If the surface of the collecting-plate is large, say several 

 square centimetres, the potential-difference existing between 

 it and the positive electrode is not found to be so much 

 reduced by attempting to measure it with a galvanometer 

 of about 6000 ohms resistance as it is wdien the collecting- 

 wire presents, as in this lamp No. 1, only a small total 

 surface of about one square centimetre. 



§ 12. Experiment 9. — A horse-shoe carbon filament, taking 

 1*3 ampere of current at a wwking-pressure of 42*5 volts, 

 had a middle plate made of a long piece of platinum wire 

 bent up in a zigzag shape so as to form a rectangular-shaped 

 grating (see fig. 8). The object of this was to ascertain 



