ELECTRIC FIELD. 



149 



which is made use of may be understood with the help of Fig. 97 

 which shows two condensers c and C connected in series and 

 acted upon by an electromotive force. The momentary flow of 

 current through the circuit charges both condensers equally, the 

 amount of charge being, let us say, g coulombs. Then the voltage 



across c is ; and the voltage across C is -^ , that is to say, 

 c o 



the voltages across the respective condensers are inversely pro- 

 portional to their respective capacities, and by varying the capaci- 

 ties (which can be done, say, by changing the sectional area of 

 the dielectric) the total voltage can be subdivided between c 

 and C in any way that is desired. 



The design of the condenser type of bushing is shown in Fig. 98. 

 The insulating material is laid on in layers of equal thickness, 

 the length (parallel to the central rod) of each successive layer 



end view 



side view 



Fig. 98. 



being reduced in proportion to the increase of its circumference, 

 so that the area of each layer is the same. Furthermore a sheet 

 of tin foil covers each successive layer of insulating material, 

 and therefore these successive layers of tin foil together with the 

 intervening layers of insulating material constitute a number of 

 condensers of equal capacities all connected in series. In this 



