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XIII. Electrostatic Investigations, especially relating to the 

 Division of Induction in the Differential Inductometer and 

 in the Electrophorus. By Dr. James Moser*. 



The Differential Inductometer. 



IN the year 1838 Faraday completed his experiments on 

 Specific Inductive Capacity, thus virtually repeating the 

 investigations of Cavendish, published some sixty years before. 

 At the end of his communication Faraday gave a description 

 of an apparatus, the " Differential Inductometer," for the 

 determination of such inductive capacity. 



This serves as the point of departure for the following in- 

 vestigation ; but I shall first, and chiefly, consider the electro- 

 static induction in a single medium, namely the atmospheric 

 air ; so that the question of " specific induction," a question 

 involving more than one medium, will be considered later. 



Faraday, in his ' Experimental Researches '(§ 1307), de- 

 scribes the above-mentioned apparatus as follows : — " Three 

 circular brass plates about five inches in diameter were 

 mounted side by side upon insulating pillars. The middle 

 one ( A ' was a fixture; but the outer plates ' B ' and c C ' 

 were moveable on slides, so that all three could be brought 

 with their sides almost into contact or separated to any re- 

 quired distance. Two gold leaves were suspended in a glass 

 jar from insulated wires. One of the outer plates, ' B,' was 

 connected with one of the gold leaves, and the other outer 

 plate with the other gold leaf. The outer plates B and C 

 were adjusted at the distance of an inch and a quarter from 

 the middle plate c A;' and the gold leaves were fixed at two 

 inches apart. ' A ' was then slightly charged with elec- 

 tricity, and the plates ' B ' and ' C ' with their gold leaves 

 thrown out of insulation at the same time, and then left in- 

 sulated. In this state of things c A ' was charged positive 

 inductrically, and B and C negative inducteously ; the 

 same dielectric (air) being in the two intervals, and the gold 

 leaves hanging, of course, parallel to each other in a relatively 

 un electrified state." 



Faraday affected the relation of the induction from A to B 

 to the induction from A to C by the introduction of various 

 dielectrics. I vary such relationship by altering the distance 

 between B and C from A. 



Faraday brought a plate of shellac between the middle 

 plate A and one of the outer plates, B. Thereupon the gold 



* Communicated by the Physical Society. 



