Farwell — Wilson Tilted Electroscope. 



319 



Akt. XXYI. — Note on the Use of the Wilson Tilted Electro- 

 scope ; by H. W. Farwell. 



In using the tilted electroscope I have frequently been 

 annoyed by the lack of steadiness of the zero of the leaf and 

 have found various causes for the wandering. Of these I will 

 mention one which I have not seen described, although very 

 likely many who have used electroscopes adjusted to a position 



Fig. 1. 





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very near to unstable equilibrium may have had the same 

 -trouble. 



The wandering which had been ascribed to defective insula- 

 tion began to show some relation to the deflections of a gal- 

 vanometer connected with a thermocouple placed near the 

 electroscope case, and on making observations with a 16 c. p. 

 carbon lamp as a heater, the disturbance was soon shown to be 

 due to convection currents inside the electroscope. The pos- 

 sibility of such a source of disturbance had been considered far 

 too remote, but the curve given above shows how distinct is 

 the relation. The lamp in this case was placed a short distance 

 above the thick lead box which contained the electroscope. 



