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



Table II. A. 



Obser cations on the Periodic Variation of the Intensity of the 

 Light of an Alternating Current Arc. 



Light from centre of Arc. Medium Arc. 



Frequency = 50 ^. 



Length of arc ... . . . ... = 0*63 cm. 



Potential-difference (P.D.) of carbons V__ qq ij. 

 (mean square value) . . . . . . J~ 



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



- Power expended in arc . ' =546 watts. 



Pressure at alternator terminals . . . =99 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. 









+ 19-8 



4-44 



10 



44 





20 



+ 14-1 



4-38-5 



32 



13 



Arc out. 



40 



+ 6-3 



+27 



55 



11 



„ „ 



60 



4- 2-7 



4-10-5 



77 



18 





80 



- 22 



-16 



100 



17 





100 



- 6-3 



-36 



122 



45 





120 



-13-5 



-37-5 



144 



74 





140 



-18-3 



-47 



165 



68 





160 



-19-8 



-54 



187 



52-5 





180 



-19-5 



-54 



208 



32 





200 



-14-8 



-50 



230 



8-5 





220 



- 7-9 



-34 



252 



9 





240 



- 1-9 



-11-2 



273 



11 



Arc out. 



260 



+ 1-9 



+13 



294 



26 



»> >> 



280 



+ 7'2 



+31 



315 



(71)? 





300 



+126 



+36 



336 



68 





320 



+19-5 



+40 



356 



42-5 





340 



4-21-7 



+473 



348 



68 





360 



+19-8 



+46-3 



327 



45 





N.B.— Owing to an accidental shift of the brushes, in this table the angle 

 corresponding to the instantaneous light is not the same as that corresponding 

 to the current. The position of the curve of instantaneous light with regard 

 to the E.M.F., current, and power curves cannot therefore in this case be 

 determined. 



