Note 30: inequality of opposed condensed charges 423 



NOTE 30, ART. 560. 



Excess of redundant fluid on positive side above deficient fluid on 

 negative side of a coated plate. 



When two equal disks have the same axis, the first being at potential V 

 and the other connected to the earth, the algebraic sum of the charges of the 

 two disks is just half the charge of the two disks together if they were both 

 raised to potential V. 



If the two disks are very near each other, the charge of the two together is 

 very little greater than that of one by itself at the same potential. 



Hence the excess of the redundant fluid above the deficient, when one of 

 the disks is raised to potential V and the other connected with the earth, is 

 very little greater than Tr~ l aV , where a is the radius. (See Note 4.) 



NOTE 31, ART. 573. 

 Intensity of the Sensation produced by an Electric Discharge. 



Cavendish tried this and several other experiments (Arts. 406, 573, 597, 

 610, 613) to determine in what way the intensity of the sensation of an electric 

 shock is affected by the two quantities on which the physical properties of the 

 discharge depend, namely the quantity of redundant fluid discharged, and the 

 degree of electrification before it is discharged, the resistance of the discharging 

 circuit being supposed constant. 



He seems to have expected (Art. 597) that the strength of the shock would 

 be "as the quantity of electricity into its velocity," or in modern language, as 

 the product of the quantity into the mean strength of the current of discharge. 

 Since the electromotive force acting on the body of the operator is measured 

 by the product of the strength of the current into the resistance of the body, 

 which we may suppose constant, Cavendish's hypothesis would make the in- 

 tensity of the shock proportional to the work done by the discharge within the 

 body. 



According to this hypothesis, if a jar charged to a given degree produces 

 a shock of a certain intensity, then a charge equal to n times the charge of this 

 jar, communicated to n 2 similar jars, and discharged through the same resistance, 

 would give a shock of equal intensity. 



By the experiment recorded in Arts. 406 and 573, in which n = 2, it appeared 

 that the shock given by four jars charged with the electricity of two jars, was 

 rather greater than that of a single jar. 



In the experiment in Art. 610 Cavendish compared the shock of jar I 

 electrified to 2j, with that of B + 2.A electrified to the same degree and com- 

 municated to the whole battery. Here the capacity of B + 2A was equal to 

 6 times jar i, and that of the whole battery was 154 times jar i, so that 6 times 



