STRIKING DISTANCE. 197 



equivalent distance from the point to the conductor is determined, 

 so that the discharges take place either by the brush of the safety- 

 valve or by a spark between the balls. The knobs of the discharger 

 are then pulled apart, the conductor B is put to earth, and the 

 point is connected with a sphere A which acts inductively on an 

 oscillation apparatus (820), and the machine is turned so as to 

 obtain a continuous brush. The time of oscillations gives then the 

 potential in absolute value for each distance of the points to the 

 conductor B, and therefore for the corresponding distances of the 

 spark discharger. This arrangement is still insufficient in the case 

 of great striking distances. A long spark may in such cases be 

 balanced by a sum of other and shorter sparks. A series of Leyden 

 jars are connected in cascade (Fig. 157), and connections are so 

 made that the two coatings of each jar are connected to the two 

 knobs A! and B 1? A 2 and B 2 , placed opposite each other and at the 

 same distance d. The outer coatings A l and B 6 being connected 

 with the two knobs of a spark discharger, if the discharge takes place 

 indifferently by all the jars in the battery or by the discharger, the 

 difference of potential between the knobs of the discharger is equal 

 to the sum of the known differences relative to all the jars in the 

 battery, or to the product of one of them by the number of jars. 

 The following table contains the results of experiments for balls 



22 mm. in diameter: 







Difference of Potential 



Striking ' -r " - ;-s v 



OT 



0*5 89*1 26730 178*2 



1*0 162 48600 162 



1 '5 190 57000 127 



2 2l6 64800 1 08 



3 2 5 6 76800 85-3 



4 291 77300 727 



5 316 94800 63-2 



6 338 101400 56-3 



7 359 107700 51-3 

 375 112500 46-9 



9 386 115800 42-9 



10 397 119100 397 



12 412 124200 34-3 



15 426 127800 28*4 



