332 



Prof. J. A. Fleming and Mr. J. E. Petavel 



Table III. A. 



Observations on the Periodic Variation of the Intensity of the 

 Light of an Alternating Current Arc. 



Light from centre of Arc. Medium Arc. 



Frequency . . . « = 26 ~. 



Length of arc = 0*63 cm. 



Potential-difference (P.D.) of carbons ") _ q 7 ii. 



(mean square value) J ~ 



Current (mean square value) .... =14 amperes. 



Power expended in arc =518 watts. 



Pressure at alternator terminals . . . = 62 volts. 



Angle 



of 

 Phase. 



Current 

 through Arc 



(instanta- 

 neous value). 



P.D. 



of Carbons 

 (instanta- 

 neous value). 



Angle 



of 

 Phase. 



Intensity of 



Light from 



Centre of 



Arc. 









+ 19 



+ 48 



7 



45 





20 



+ 12-5 



+395 



28 



26 





40 



4- 5-8 



+21-5 



49 



6 



Arc out. 



60 



+ 0-5 



+ 2-5 



71 



12 



>> »> 



80 



- 2-2 



-22-5 



92 



7 



JJ JJ 



100 



- 9-7 



-24 



114 



14 



Arc just starting. 



120 



-16-8 



-34-5 



136 



67 





140 



-195 



-455 



158 



71 





160 



-21-8 



-47-5 



180 



66 





180 



-193 



-50 



202 



24 





200 



-11-5 



-42 



224 



19-5 



Arc out. 



220 



- 4-8 



-22 



246 



4 



»> >> 



240 



- 05 



_ 2 



268 



8 



» u 



260 



+ 20 



+ 17 



290 



22 





280 



+ 10-8 



+26 



312 



40 





300 



+ 15-8 



+36 



333 



57 





320 



4-207 



+47-5 



354 



75 





340 



4-21-3 



+50 



15 



53 





360 



4-19 



4-48 









340 



4-21 



+51 



345 



62 





320 



4-20 



+48 



323 



70 





