Mr. 0. J. Lodge. Experiments on 



[June 4, 



Sparking Distance between Plates in the Different Cases. 



Unless the jars are large, compared with the capacity of the plates, 

 even the conditions of fig. 9 will not make the rush quite sudden ; 

 and in that case points and small knobs do get struck more easily 

 than large knobs and domes, especially when the top plate is nega- 

 tive.* But when the rush is really sudden, no difference as to sign 

 manages to show itself ; and even such insignificant advantage as the- 

 point happens to show in the first column of the above table dis- 

 appears. 



High resistance, interposed between knob and bottom plate in 

 fig. 10, alters the character of the spark entirely, making it soft and 

 velvety, but has no effect upon its length nor upon the ease with 

 which its knob gets struck as compared with others connected direct. 

 But the same resistance, interposed in fig. 9, prevents its being struck 

 altogether. 



In other words, sudden rushes strike good conductors, independent 

 of terminal : steady strain selects sharp or small terminals, almost 

 independent of conductivity ; the violence of the flash being, how- 

 ever, by high resistance very much altered. The total energy is, 

 doubtless, the same, or even greater with the quiet heating spark, 

 because of concentration and no loss by radiation ; but the duration 



* This fact has been explained by Mr. Wimshurst, ' Journ. Inst. Elec. Engineers,' 

 1880, page 482. 



