liuiuct'ioih Motor 159' 



These values are plotted in Fi<;iire 1, in the "calculated" 

 curve. 



Experiment (b). — Further experiments of the same nature were 

 carried out by removing the armature from a series wound " Im- 

 misch " motor, and replacing it by a hollow copper cylinder with 

 an iron core. The pole pieces were built up with cast iron so as 

 to clear the copper by about one millimetre. The whole was- 

 mounted on a cradle dynamometer, and arranged so that the copper 

 cylinder could be rotated at different speecLs by means of a belt 

 and pulleys of different sizes. 



Current was passed through the field coils and the torque pro- 

 duced on rotating the copper measured in the usual way. 



The value of </> was measured by making and breaking the cur-^ 

 rent in the field coils, and noting the deflection of a fluxmeter with 

 an exploring coil, wound around the copper. In each case the- 

 couple with zero flux was measured to eliminate the frictional 

 couple. The following results were obtained : — 



_ , ,. v„\„a rst JIass of Distance of Couple due to Couple corrected 



Revolution \alueof ^,,^\^,,^- Hderfrom Eddv ."^ to 



per second. 2<^ rider. Centre. Currents. ^=2-79xl05/2 



6-6^ 2.72 xlO« 200 52.5 cm.) '•45xl0« /.84x10B 



11 /^ 100 10 cm. ^ 1 r.O 1A7 1 TO 1 AT 



11-0 2.74x10= 200 60 cm. ) 1-08x10^ 1.12x10^ 



16.1 o-n ,n5 onn -n """ ' 1.23x10^ 1.23 X 10^ 

 2.79 xlO^ 200 70 cm. ) 



20.2 ^.Q ^^, ]^^ i?^'"- - 1.27 xlOT 1.27x10^ 

 2.79x10= 200 73 cm. ) 



n^ A 100 10 cm. I 1 o- 1A7 1 OT 1A7 



24-0 2.79x10= 200 70 cm. , 1-2/ x 10^ 1.27x10^ 



In order to correct the observed couples for variations in the value - 

 of <^ ib was assumed that the couple is proportioned to <^'^. To verify 

 this, two experiments were carried out at the same rate of rotation 

 with values of <^ in the ratio of 1 to 2. The couples were measured as 

 before. The values of the ratio Couple :^'^ were found to be 



6.07x108 and 6.04 Xl0«. 



This justifies the assumption made. 



The values of the couples corrected in this way are given in the 

 last column of the table, and are plotted against revolutions per- 

 second in Fig. 2. 



