114 



Mr Whiddington, The Shadow Electroscope 



experiment. The above table gives the results of an experiment. 

 From which the mean value of V1/V2 comes out to be 1'322. 



By calculation from this value Cj, = 194-7 cm. 



Assuming the identical dimensions of the two condensers* the 

 Specific Inductive Capacity of Ebonite is just the ratio 



fi iri _ 194-7 



^' '^ 65-0 



= 2-98. 



A value not far removed from the accepted value which ac 

 cording to the table of Kaye and Laby will usually lie between 

 2-7 and 2-9. 



Experiment 4. The comparison of two capacities by the ioniza 

 tion leak method. 



It is convenient to illustrate this method by giving as an 

 example the results of an experiment using the same two con 

 densers as the preceding experiment. 



Method. If when the lime coated spiral is glowing steadily the 

 slow leak of the electroscope be observed firstly with C'^ in position 

 and then with Cj, in position, the capacities can at once be compared, 

 for if Ta and T^ be these times it can be shown that 



^g + ^e _ Tg 

 Cb + ^e Tj, 



The following table gives some results obtained with this 

 method. In order to eliminate as far as possible any variations 

 in the amount of ionization (which depends very greatly on the 

 temperature of the filament and therefore on the e.m.f. of the 

 power supplying cell) the readings for T^ and Tj, were taken 

 alternately and as quickly as possible. It will be seen that under 



* This can easily be tested experimentally. 



