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



Take Diagram 3, in which No. 2 machine is a motor. The total 



field = jjj^ x x = ^'15 x 10 6 lines of induction. Since the area 



5*15 



of the diagram is 53*5 sq. cm., an ordinate of 1 cm. = x 10 6 = 



96 x 10 4 lines of induction in 10°. Hence, an ordinate of 1 cm. 



9-6 x 10 4 



represents an induction of ^g.g — = 1400 lines per sq. cm. The 



difference between ordinates at 320° and at 230° is 2'0 ; hence, the 



difference of induction is actually 2800. Theoretically, we have 



2/cmC _ 3} x 104 x 11-4 ORaR . , OQAn ' ' J 



— ^ = 2boo, as against 2800 actually observed. 



In Diagram No. 4, No. 1 machine is a generator. The total field 

 52 1 



= X -jT^r x 10 8 = 3'97xl0 6 lines. The area of the diagram is 



3'97 



90'9 sq. cm., and therefore an ordinate of 1 cm. = ^q.^ x 10 6 = 4*37 



X 10 4 lines in 10°. Hence, an ordinate of 1 cm. represents an induc- 

 4 - 37 x 10 4 



tion of — — = 639 lines per sq. cm. The difference between 



ordinates at 50° and at 140° is 4*5 ; hence, the difference of induction 



2mC 3^x104x12-9 

 is actually 2877. Theoretically, we have — ^ — = = 



3010, as against 2877. 



In Diagram No. 5, No. 2 machine is a motor. The total field 

 63*5 1 



= x j"2^ x 10 8 = 4*96 X 10 6 lines. The area of the diagram is 



