[ 107 ] 



XIV. On the Explosive Distance of the direct induced Current be- 

 tween Electrodes of the same kind. By M. Elie Wartmann *. 



THE greatest striking-distance which can be realized with a 

 given electrical machine takes place when the largest 

 possible quantity of electricity is accumulated at the point of the 

 conductor from which the spark emanates, and when the accu- 

 mulation takes place with sufficient slowness to prevent any of 

 the fluid escaping before the discharge. As the thickness of the 

 electric layer is modified by the dimensions and the form of the 

 body which is brought near, it is evident that the maximum stri- 

 king-distance corresponds to a given discharger. Thus Pfaff used 

 a ball 8 inches in diameter to draw sparks 18 inches long 

 from a machine the conductor of which was terminated by a 

 4-inch ballf. Faraday found that the spark extended furthest 

 between two balls of unequal size when the smaller ball was 

 charged positively by induction^. M. Riess has shown that these 

 results are not general, and depend upon the construction of the 

 machine employed §. 



In RuhmkorfFs apparatus, when the ends of the induced cir- 

 cuit are so far separated that the interposed air only allows the 

 direct current generated by the opening of the battery to pass, 

 facts similar to the above are established. It is well known, for 

 instance, that the striking-distance between a point and a plate 

 is greater when the point is positive than in the opposite case. 

 But what happens when the electrodes are of the same kind and 

 of exactly similar dimensions ? I do not believe that this ques- 

 tion has hitherto been examined. 



To supply the answer, I used a bobbin, 0*352 metre in length 

 and 0*165 metre in diameter. The power of the effects which 

 it is capable of producing shows the perfect isolation of the 

 layers of covered wire, which measures about 9000 metres. It 

 is a partitioned machine, furnished with a Foucault's amalga- 

 mated platinum break, and was worked with a battery of from 2 

 to 10 Bunsen's elements, the large size. 



The pairs of similar electrodes between which the spark was to 

 pass were screwed to the arms of a Henley's universal discharger. 

 Every possible care was taken that their form and dimensions 

 should be exactly alike. These electrodes consisted successively 



* Translated by Dr. Griffith, from the Bibliotheque Universelle, 1865, 

 p. 236. 



t Gehler's Neues Worterbuch, vol. iii. p. 464. 



X Experimental Researches, Series XIII. §§ 1435 to 1489. Phil. Trans, 

 for 1838, p. 126. 



§ Die Lehre von der Reibungselektricitat, vol. i. p. 2/6 ; and vol. ii. 

 p. 129. 



