1878.] the Photometry of the Magneto-Electric Light. 165 









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The following is a statement, furnished me by Captain R. Y. 

 Armstrong, R.E., of the electrical conditions of the circuit. 



The resistance of the stationary wire = 4*46 ohms. 

 „ „ magnetizing coil = 0*44 ohm. 



In the generator the resistance of the light- circuit coil = 0'24 ohm. 



The light coils were in divided circuit, as were also the right and 

 left stationary coils. 



When driven at from 375 to 383 revolutions, the resistance of the 

 voltaic arc was about 0T8 ohm; the other resistances in the circuit 

 were 0*7 ohm. The electromotive force of the machine when driven 

 at the above speed was 111 volts, a measure which has been arrived 

 at by Captain Armstrong from other experiments. The electromotive 

 force between 375 and 383 revolutions of the armature was assumed 

 to vary as the number of revolutions, an assumption which was borne 

 out as practically correct by other measurements made for the purpose. 

 In order to ascertain what effect the insertion of resistance had on the 

 current, the following experiment was undertaken by Captain Arm- 

 strong with a smaller form of gramme machine, called Machine No. II. 



