RECENT PROGRESS IN PHYSICS. 



407 



We shall see presently that this coefficient docs not depend on the 

 distance of the plates alone. 



The determination of the density of the electricity on C hy means 

 of the spark micrometer renders the result very apparent, hut is not 

 suitahle for accurate determinations, hecause the knob of the microni- 

 eter connected with the ground influences the induction of electricity 

 on the opposite one. Instead of the spark micrometer, however, any 

 other method of measuring the electrical density on C may be used. 



Biess applied the torsion balance in a more accurate series. He 

 found in this manner that when an electrical charge was impartedto 

 the insulated system D B, (the knob of the micrometer connected with 

 the ground being removed,) the condenser being away, and unity 

 representing the electrical density of C, on the approach of the con- 

 denser at different distances, the density on C was as follows : 



Distance of plates. 

 Density on C 



2 lines. 

 0. 173 



3, 

 0.235 



4. I 6. 

 0.286 0.335 



10. 



15. 



0.492 0.595 



20. 

 0.683 



50. 

 0.897 



00 



1 



These results correspond very well with those found by means of 

 the spark micrometer. 



When the connecting wire between B and C was shortened, the 

 foUowins; somewhat different numbers were found : 



Distance of plates. 

 Density 



2 lines. 

 0.155 



3. 



0.219 



4. 

 0.274 



5. { 10. 

 0.30610.488 



15. 

 0.630 





20. 

 0. 688 



50. 



0.888 



CO 



On the back of the collector the electrical density was diminished 

 by the proximity of the condensor. Biess found that on this surface, 

 near its edge^, the density was diminished in the following proportion: 



Distance of plates. 

 Density 



2. 

 0.260 



3. 

 0.341 



4. 



0.412 



0.460 



10. [ 15. ( 20, 

 0. 617 [0. 71D|0. 028 



50. f 00 

 0.941} 1 



Thus it appears that on the back of the collector, near the e^ge, 

 the density of the electricity is diminished by the proximity of the 

 condenser far less than at the end C of the connecting wire, placed in 

 the middle of the plate ; hence the coefficunt of accumulation of the 

 condenser is less ivhen the body to he examined is placed at the edge than 

 lohen at the middle of the collector.^ 



* This conclusion does not seem to me perfectly correct. The experiments show that 

 ■when the constant source of electricity is kept at C the coefficient of accumulation 

 decreases more than when the back surface of the collector is touched near tlie edge hy 

 the constant source of electricity. That it is the same whether the knob C or the middle 

 of the collector it.sclf be touched by the constant source is not yet proven, as it must be 

 before the above conclusion can be admitted. 



