RECENT PROGRESS IN PHYSICS. 423 



For s=4, d^=2, we have q = U.5, q' =: 12.5, hence 



n' 12 5 



-1= -- =0.862. 

 q 14.5 



Thus it is evident that, under the most different circumstances, very 

 nearly the same portion of the entire charge disappeared on discharg- 

 ing at the striking distance. As a mean of all the experiments pre- 

 sented in the last "two tables, it appears that 0.846 or \^ of the entire 

 charge disappears after discharge at the striking distance, whether 

 good or bad metallic conductors are used^ and consequently y-V of the 

 entire cliarge remain as residue. 



When liiess substituted parallel metallic plates for the knobs on the 



spark micrometer, an experimental series gave for -i- the mean value 



0.849 ; and when an interruption of 0.3 line was made in the closing 



circuit, he had — =: 0.842, or almost exactly the same value for the 



quantity of electricity disappearing at the striking distance. 



The value — is probably dependent upon the thickness of the glass 

 q 

 of the battery, but no experiments have as yet been made to deter- 

 mine this. 



§ 34. Results by the ordinary mode of discharge. — From these ex- 

 periments we may easily determine what takes place in the ordinary 

 mode of discharge, in Avhich a movable knob, connected with the outer 

 coating, is brought into contact with the fixed knob of the inner coat- 

 ing. When the movable knob arrives at the striking distance, which 

 we shall denote by d, {^ of the charge disappears and ^. remain ; 

 another discharge can take place only when the movable knob is ap- 

 proached to yV <^^j at which distance again }\ of the remaining charge 

 disappear ; a third discharge follows when the movable knob is brought 

 to (r-i)^ d, &c. Suppose the original striking distance to be 1^ 

 lines, the series of discharges take place at the following distances : 



1.5 ; 0.23; 0.035 ; 0.0055 lines; 

 the third of which does not differ sensibly from contact. In the ordi- 

 nary mode of discharge, therefore, the closing circuit receives several 

 discharges, one after another. 



§ 35. Results by discharge at the strhqng distance. — In discharge 

 at the striking distance so great a quantity of electricity disappears 

 that merely a small approximation of the knobs does not produce a 

 second discharge ; but the striking distance must be reduced to ^V ^^ 

 the original. That so great a quantity of electricity as fV of the en- 

 tire charge should disappear seems to indicate that the discharge, 

 even at the striking distance, is successive ; the air is rarefied by the 

 transfer of the first quantity of electricity, and thus the transfer of a 

 new portion is rendered possible, which could not have taken place if 

 the resistance to be overcome had not been diminished by the rarefac- 

 tion of the air. The passage of electricity continues until the charge 

 of the battery has become so feeble that at the constant distance of the 



