254 Mr. R. H. M. Bosanquet on Practical Electricity. 



-9 side cells- 



21-5 volts between magnet-terminals. 



Magnets Magnets 



Armature 



12 principal cells 



28-1 volts between armature- terminals. 



In this case I had a balance when 9 amperes of current 

 were passing in each circuit. 



It is clear that the current through the magnets is due to 

 the difference of tensions between the two sets of cells ; con- 

 sequently, 



volts. 

 Tension of 12 cells = 28'1 (measured) 

 ,, J ,, =zl"0 ,, 



and, dividing by the measured current of 9 amperes, we find 

 •73 ohm for the resistance of the magnets. This corresponds 

 well with my direct measure of '74, and less well with the 

 resistance given by the makers, "77. 



The balance is a function of the current ; and if the power 

 in action be varied, the current in the principal cells changes 

 faster than that in the magnet circuit (or side cells). It is 

 to this circumstance that the stability of the arrangement is 

 due. 



In order to give foundation for the theory of this arrange- 

 ment we have to represent the variation of the tension of the 

 cells with varying current. We may represent the course of 

 the changes sufficiently for this purpose, according to my 

 measures, by assuming that the tension varies with the 

 charging current, so that it is 1*9 volt per cell when at rest 

 and 2*4 per cell when the current is 10 amperes, i. e. it varies 

 2*0 volt per cell per ampere. The same rule expresses fairly 

 well the diminution of tension when the freshly charged 

 battery gives out a current. I shall return to the question 

 of the rationale of this, and for the present assume general 

 values, and that the change of tension is proportional to the 

 current. 



