614 



Mr. J. Viriamu Jones 



[May 24, 



number of layers of thin sheet and controlled by a spring, brush and 

 disc circumference being well amalgamated. This was not at all 

 successful. Trials were then made with amalgamated copper and 

 amalgamated lead, and with the substitution of a dead- weight pressure 

 for a spring. But no satisfactory result could be obtained. 



It was noticed, however, that after amalgamation the readings 

 were fairly steady for a short interval, and it seemed likely that if 

 mercury could be continuously supplied to the surface of contact 

 between the brush and disc the electromotive-force at their contact 

 would be rendered much more constant. This led on to the idea of 



Fig. 5. — Part end View. 



a brush consisting of a single wire, perforated by a channel through 

 which a constant flow of mercury might be maintained from a cistern 

 of adjustable height, and a brush of this description was made (Fig. 5). 

 Trial showed that our difficulty was at an end. The variations almost 

 disappeared, the sudden jumps quite ceased to trouble us, and the 

 motion of the needle did not extend over more than one or two 

 divisions of the scale for many minutes. A multiplication of such 

 brushes round the circumference would make still further improve- 

 ment. 



