[ 291. ] 



XXXII. On the Measurement of Changes in Resistance by a 

 Valve Method. By K. T. Beattv, M.A., /KSc, Lecturer 

 in Physics, and A. Gilmour, M.Sc, 1851 Exhibition Student y 

 Queen's University, Belfast*. 



WHEN a valve circuit is arranged, as in fig. 1, to 

 generate oscillations, it is well known that on the 

 insertion of a high resistance shunted by a condenser, in 

 series with the grid, the oscillations will be broken up into 

 equally spaced groups, and the groups thus formed will give 

 rise to a note whose frequency will be equal to the number 

 of interruptions per second. 



If the frequency of the note be plotted against the grid 

 resistance R (fig. 1) a curve is obtained showing decreasing 

 frequencv with increasing R, and when R is very large the 

 sound in the telephone may only occur, perhaps, once per 

 minute. 



Fte. 1. 



It is the purpose of this paper to show that such a curve 

 only represents the final stages of a series of relations between 

 R and the frequency f, and to exhibit these relations over a 

 wide range of values of R. 



Experimental A rrangements. 



The experimental circuit used is shown in fig. 1. A re- 

 ceiving valve maintained oscillations in the main circuit LK. 

 A variable liquid resistance R (copper sulphate solution in 

 * Communicated by the Authors. 



