Intelligence and Miscellaneous Articles, 557 



definite problems. But it follows from preceding considerations, that 

 the lower limit of these charges is precisely what is called the induc- 

 tive capacity. 



In the above-mentioned note I have occupied myself in deter- 

 mining the higher limit of the charge ; in the present one my prin- 

 cipal concern is with the lower limit. In both cases I have followed 

 the same method of experimentation. I constructed a series of ful- 

 minating panes of the same dimensions with different dielectrics ; I 

 charged them successively by putting them for a given time in com- 

 munication with a source of electricity of constant tension, and in 

 each case measured the quantity of electricity condensed by the 

 inducing armature by what I have called the method of gauging. 



Working in this way, I have found that the quantity of electricity 

 condensed diminishes with the duration of the charge, even when 

 only small intervals of time are considered. Thus the following 

 numbers were obtained for the charges of a condenser made of com- 

 mercial stearic acid, the charge of an air- condenser of the same size 

 being taken as unity : — 



Quantity of electricity 

 Duration of the charge. condensed. 



A fraction of a second 1*3 



2 seconds 1*8 



40 seconds 2*7 



Several hours 7"0 



Hence if the conductibility and inductive capacity are two distinct 

 properties, it will be necessary, in order to eliminate the first, to 

 work more rapidly than I have done. Physicists who have worked 

 on the inductive capacity have not usually noted the time during 

 which their condensers were charged. Faraday merely mentions 

 that he worked rapidly ; but I think that at least three or four seconds 

 would be needed to execute the manipulation which his method 

 requires ; and it is indubitable that during this interval conductibility 

 may manifest its action, since, in the example cited, the quantity of 

 electricity condensed where the duration of the charge is 2 seconds 

 is four times as much as with a charge whose duration I estimate at 

 ^-^th of a second. 



I have not yet reduced the duration below this fraction of a second ; 

 but I consider it certain that in this small interval of time conducti- 

 bility may exert a certain action, and I am led to believe that for 

 stearic acid the true value of the lower limit of the charges is unity, 

 which amounts to saying that stearic acid has exactly the same in- 

 ductive capacity as air. 



All the insulating substances I have worked with have not com- 

 ported themselves like stearic acid, and some of the results obtained 

 appear at first to furnish a decisive argument in favour of Faraday's 

 theory. Thus, with two fulminating panes of the same size, one of 

 sulphur and one of stearic acid, I found that the latter exceeds the 

 former when the duration of the charge is some seconds, but that 

 the former decidedly preponderates over the latter when the duration 

 of the charge is reduced to y-J^-th of a second. At first sight it seems 

 impossible to explain this inversion without introducing some pro- 



Phil Mag, S. 4, No. 171, Buppl Vol. 25. 2 P 



