1883.] On the Electrical Resistance of Carbon Contacts. 



3 



Pressure. Kesistance, 



Grammes. Olims. 



2-5 5-90 



3 5 13 



3 5 5*00 



4 : . . 4-60 



4*5 4-33 



5 4-23 



7*5 3-53 



10 3-06 



12-5 ........ 2-80 



15 2-60 



17 5 2-46 



20 2-33 



25 2 16 



50 1-86 



From the above results the curve fig. 2 has been constructed, where 

 the abscissas represent the pressures at the points of contact and the 

 ordinates the resistance in ohms. The curve shows clearly that the 

 greatest variations occur when the pressure is small and the resistance 

 comparatively high. 



4. Change of Resistance partly due to Effect of Current, 



In making measurements of the kind above described, the details 

 of the arrangements were from time to time varied. Different pro- 

 portional coils were used and different numbers of battery cells ; and 

 it soon became evident that the resistance of the carbon contact was 

 largely dependent on the strength of the current used to measure it. 

 In Table II (giving the mean of two series of observations) is shown 

 the result of using one, two, three, and four cells successively. 



b2 



