466 Mr. B. 0. Peirce on the Spark produced in 



Separation of 

 plates. 



Deflections. 



Separation of 

 plates. 



Deflections. 



millim. 





milim. 





•050 



183 



•800 



91 



•100 



176 



•850 



95 



150 



164 



•900 



96 



•200 



145 



•950 



88 



•250 



130 



i-000 



93 



•300 



136 



1050 



79 



•350 



123 



1100 



85 



•400 



127 



1150 



84 



•450 



120 



1-200 



70 



•500 



106 



1-250 



75 



•550 



102 



1-500 



63 



•600 



97 



1-750 



51 



•650 



92 



2000 



50 



•700 



88 



2-250 



45 



•750 



90 



2500 



42 



When the sparks passed between the ends of two copper 

 wires § millim. in diameter, carefully filed so as to be parallel, 

 the curves obtained were very regular, but of the same general 

 shape. As an example I give the following : — 



Distance over which 

 the spark leaped. 



Deflections. 



millim. 





1 



90 



2 



70 



3 



55 



4 



44 



5 



35-6 



6 



27 



7 



20 



8 



13 



9 



7 



10 



25 



11 



1-4 



12 



•8 



Sir William Thomson has shown, in his paper " On the 

 Electromotive Force necessary to produce a Spark," that a 

 greater force per unit of length is needed for short distances 

 than for long distances. He does not state in his paper 

 whether he experimented upon the Ruhmkorff coil or the 

 Holtz machine. In using the quadrant electrometer in mea- 

 suring the electromotive force of the sparks from an induction- 

 coil, it is, of course, necessary to use a small leaping-distance 

 for the sparks, to avoid the return current. At times I have 



