288 THE OUTGO OF ENERGY 



The meniscus will be displaced in the direc- 

 tion indicating a higher potential at the middle 

 or " equator " of the longitudinal surface than 

 at the cross-section. Note the divisions of the 

 scale, traversed by the meniscus the displace- 

 ment is proportional to the difference of potential. 



2. Move the electrode on the longitudinal sur- 

 face a few millimetres towards the cross-section. 

 Determine the difference of potential here. It 

 will be less than before. Measure the potential 

 in similar manner at intervals of 5 mrn. between 

 this point and the cross-section. On co-ordinate 

 paper set down on the abscissa the number of 

 millimetres from equator to cross-section. Set 

 down as ordinates the number of divisions of the 

 micrometer scale traversed by the meniscus when 

 the electrode on the longitudinal surface is placed 

 successively on the equator, and at intervals of 5 

 mm. between equator and cross-section. Draw 

 the curve uniting the summits of the ordinates. 



As the cross-section is approached, the curve of 

 potential will fall more and more rapidly. The 

 centre of the cross-section is negative towards 

 the outer parts of the section. Points on the 

 equator, or equidistant from it, have the same 

 potential. Points on the longitudinal surface 

 at different distances from the equator, and on 

 the cross-section at different distances from the 



