and its Effects. 133 



ciently near to the other, broad, loud sparks will be obtained, 

 which far surpass the thin iuduction sparks in splendour and 

 strength, although they are inferior to them in length. This 

 difference in the sparks is most perceptible when the poles are 

 within the spark-distance from the coatings ; three series of 

 sparks are then obtained, of which two charge the jar and one 

 discharges it. It is evident that charges and discharges are here 

 only apparently simultaneous ; actually, they follow one another 

 at intervals too small to be recognized by the eye*. 



A curious modiiication can be made in the experiment, by 

 connecting the discharging wire not immediately with the coat- 

 ings of the jar, but at any points of 

 the mres which connect the jar with 

 the poles. Let P and N in the ad- 

 joining figure be the poles of the 

 induction coil PN, a and b be the 

 coatings of the jar, and Vb and N« 

 the wires connecting the same with 

 the poles ; the discharging wires can 

 be connected at any points cc of these 



latter wires ; indeed they may proceed from the poles P and N 

 themselves, and the intense discharge spark will be obtained at 

 the point of interruption del. But, of course, these sparks will 

 be weaker the longer the paths acd and bed, or, more correctly, 

 the more resistance these paths oppose. If wires are here in- 

 serted which are equal in length or resistance to the induction 

 wire itself, then all difference between the discharge sparks and 

 the induction sparks vanishes. Cateris paribus, the discharge 

 sparks are stronger the more powerful the battery and the 

 smaller the charged surfaces, as might be predicted from the 

 former experiments of lliess with jars laden by the electrical 

 machine. 



With respect to the reason why the induction current fails 

 permanently to charge a Leyden jar, even when the former acts 

 only by means of sparks, I was at first inclined to believe that, 

 in consequence of a transmitting action of the glass, a discharge 

 took ])lace ; the phajnomena with the glass plates coated on one 

 side seemed favourable to this opinion. I have since convinced 

 myself, however, that the cause is rather to be sought in the fact, 

 that, under all circumstances, even when no second connexion is 

 present, the jar is always discharged again by the induction wire 



* This oljscn'ation was communicated by me to the Beilin Academy, on 

 the 7tl> of December, after T had communicated it some weeks previous to 

 a few friends. Since then the ])ha'nomenon has been described by Grove 

 in the January Number of the Philosojjhical Magazine. During the pub- 

 lieatiou of tlie ))resent memoir, I have also learned tliat it was known to a 

 few jiersons in Berlin as early as last summer. 



