58 



Dr. J. Hopkinson and Mr. E. Wilson. [Mar. 17, 



run as a generator, and No. 2 as a motor. The magnets were in each 

 ease coupled parallel, and excited by a battery each through an 

 adjustable resistance. The two armatures were coupled in series 

 with another battery and the following observations were made : — 





Potential on 

 magnets in yolts. 



Potential on 

 brushes. 



Speed per 

 minute. 



Current in 

 amperes. 



Lead of 

 brushes. 



No. 1 



24—24 



66—67 



880 



102—103 



26° 



No. 2 



29—29 



86—84 



880 



102—103 



29° 



From which we infer : — 





Current in 

 magnets. 



4 7TOC. 



Corrected potential 

 for resistance of 

 armature. 



Total induction 

 I. 



No. 1 



1-78 



8,900 



70*8 



2 '30 x 10 6 



No. 2 



2-15 



10,750 



80-7 



2 -65 x 10 6 



As there was uncertainty as to the precise accuracy of the measure- 

 ments of potential, it appeared best to remeasure the potentials with 

 no current through the armature with the Siemens' voltmeter placed 

 as in the last experiment. Each machine was theretore run on open 

 circuit with its magnets excited, and its potential was measured. 





Potential on magnets 

 in volts. 



Potential on 

 brushes. 



Speed per 

 minute. 



Potential at 

 880 revs. 



No. 1 



25—25 



90—90 



880 



90-0 



No. 2 



28—28 



79—80 



715—710 



98-2 



From which, since the formula is reduced to 

 A 2 



I = ry- (4 7rnc—4 XmC), 



the characteristic being practically straight, we infer : — 



1 



