Intelligence and Miscellaneous Articles. 317 



denser ? It is this question that I have endeavoured to determine 

 by the following experiments. 



Two plane condensers, quite equal and famished with electro- 

 metric appendages, are connected each with one of the armatures 

 of a Holtz machine, on the one side, and, on the other, with the 

 earth. One of them is provided with a plate of glass of 1'32 mil- 

 lim. thickness ; the other receives plates of various kinds and thick- 

 nesses. The spontaneous discharges always take place at a constant 

 distance. Under these conditions the quantities of electricity 

 translated, daring one and the same time, by the number of sparks 

 furnished by each of the conjugate condensers may be regarded as 

 equal. 



The following Table sums up the results of a great number of 

 concordant experiments. The number of sparks refers to the in- 

 terval between two sparks from the standard condenser. 



^- , r- , , T , Thickness. Nimiber of 



^aUne of the plates. ^^^^j.^^_ ^p^^j^^_ 



Glass 2-15 1-5 



3-02 2 



„ 3-75 3 



„ 5-22 4 



Hardened caoutchouc .... 1 2 



.... 2 4 



Vulcanized caoutchouc . . 2 5 



„ „ . . 3 6 



4 7 



..5 9 



The rarer the sparks, the stronger they are. This can be ac- 

 counted for by the report and the light which accompany them ; 

 but it can be demonstrated also by means of a variety of the Kin- 

 nersley thermometer in which the action of the spark upon the 

 liquid is replaced by the pushing-back of an index of elder-pith. 



It is seen that the ratio of the number of sparks to the thickness 

 of the plate is sensibly constant for plates of the same nature. The 

 irregularities presented by the vulcanized caoutchouc proceed, 

 doubtless, from its want of homogeneity. 



It is morever seen how great are the differences of effect ob- 

 tained with plates of the same thickness but of different kinds. 



Besides, the ordinary laws of the discharge of a condenser are 

 very well verified by employing our conjugate condensers supplied 

 with plates of the same nature. It will be sufficient, in order to 

 comprise in Ciausius's formula the peculiarities here signalized, to 

 introduce a constant dependent solely on the nature of the dielec- 

 tric. This constant, it seems, would be no other than that of 

 Faraday ; but it will be remarked that, according to our results, 

 the greater it is the feebler is the discharge. — ComjjUs Rendus de 

 VAcademie des Sciences, September 10, 1877, tome Ixxxv. p. 547-8. 



