416 



RECENT PROGRESS IN PHYSICS. 



measuring jar. Suppose q =z S ; this means the charge of the battery 

 has been continued until 8 discharges of the measuring jar have 

 occurred. 



The density of tlie electric charge of the battery depends, not only 

 upon the quantity of E imparted to it, but also upon the size of the 

 surface over which it spreads. If the same quantity of electricity is 

 diffused over a double, treble, &c., surface, its density becomes twice, 

 thrice, &c., as small ; in short, the density of the E is inversely pro- 

 portional to the magnitude of the surface of the battery, but is directly 

 proportional to the quantity of E imparted ; tlie density upon the 

 charged battery may then be expressed by 



s 

 q indicating the quantity of imparted E, s the size of the surface. 



In his experiment, Biess used jars as nearly alike as possible, so 

 that the surface of the battery was proportional to the number of jars. 

 The surface of one jar was taken as the unit of area. 



To attain accurate results, the charge of the battery must be made 

 continuously by contact, and not by sparks passing from the conductor. 

 § 30. Repulsion of the inner coating or the battery. — If the inner 

 coating of the first jar of a battery be connected with a wire termi- 

 Fig. 49. nating in a metallic knob, as 



shown in fig. 49, the free elec- 

 tricity of this coating of the 

 charged battery will be diffused 

 over the knob. In contact 

 with the first is a second knob 

 b fastened to tlie end of a glass 

 rod, which may readily turn 

 about its middle point, and bearing at its other end a small scale pan. 

 The scale is loaded until it is in equilibrium with the knob 6. 



Tlie glass rod h was 12 inches long, and had at the middle a piece 

 witli steel pivots resting upon the rounded edges of two agate plates. 

 1^ 2, 3, 4 grains being now placed in succession upon the scales, it 

 was found what quantity of E should pass through the measuring jar 

 from the outer coating of the battery before the knob h was repelled. 

 When the battery consisted of only one jar, and 1 grain was placed 

 in the scale, repulsion followed after 2 discharges of the measuring 

 jar, 3 grains being placed in it, 4 discharges were required. 



Each experiment was repeated and the mean of the two taken. 

 The same experiments Averc then made with a battery of 2, 3, . . . 

 to 5 jars. The results are comprised in the following table : 



