538 Mr. J. J. Dowling and Miss K. M. Preston on the 



more or less in the order they were made. The time at our 

 disposal for the work did not, unfortunately, permit of the 

 observations being pushed to the highest possible accuracy, 

 but it will be evident that the new methods lend themselves 

 to measurements of considerable precision. 



§ 3. After several trials of various possible oscillation- 

 circuits, and with different values of battery voltages, etc., 

 the following was adopted as most likely to prove satisFactory 

 for the present purpose. It was made up of existing apparatus,, 

 and could, no doubt, be much improved. 



The coil AB (fig. 1) was of 170 turns bare (22) copper 



Fig. 1. 



V 



I! 



wire, wound on a 10 cm. square section frame 60 cms. long. 

 C was a graduated sector condenser (100-1200 fjifi farad), 

 An Ediswan (ES 4 ) valve was employed with a *6 ampere 

 filament current. An anode battery of 20 volts was found 

 suitable. 



A potential balancing arrangement, inserted in the anode 

 circuit, enables a sensitive galvanometer to be employed to 

 detect small variations of the anode current. 



The resistance to be measured is inserted in the oscillation- 

 circuit at H, where it has no direct-current component passing 

 through it, 



§ 4. The potential balancing device, just referred to, is 

 represented by ET (fig. 1), and the theory of its action is 

 important. It consists of a few cells (E), in series with a 

 rather large resistance (T), the whole being in parallel with 

 the galvanometer branch (GS). Let g be the resistance of 

 the (shunted) galvanometer (GS). 



If I is any value of the anode current, a current 



