22 Prof. E. Edlund on the Path of Electrical Induction- and 



coal-gas. The two former were dried, but the latter not. The 

 means only may here be given : — 



Pressure in the \ 



1 atmo- 



140 



80 



40 



20 



4 



glass cylinder. J sphere. 



mm. 



mm. 



mm. 



mm. 



mm. 





f46-0 



7-0 



15-8 



20-6 



20-9 



659 



Deflections for 



42:7 



6-5 



13-7 



. . 



, 



56-1 



atmospheric air 



^_ 



6-3 



13-7 

 17-4 









Mean . . 



44*4 



6-6 



15-2 



20-6 



20-9 



61-0 



When the pressure was reduced from one atmosphere to 140 

 millims., the deflection diminished from 44*4 to 6*6 divisions, 

 when it again increased until for a pressure of 4 millims. it was 

 greater than for one atmosphere. 



Experiments with dried carbonic acid led to an analogous 

 result j the deflection was least for a pressure of 140 millims., 

 after which it again began to increase : — 



Pressure in the ) 1 atmo- 

 glass cylinder. \ sphere. 



140 



80 



40 



20 



7 



mm. 



mm. 



mm. 



mm. 



mm. 



)eflections for f23'6 

 carbonic acid \ 



3-4 



15-1 



70 



11-9 



15 



5-0 

 3-2 



19-9 

 17-8- 



8-7 

 7-9 



16-5 

 14«2 





Mean . . 23*6 



15-0 



140 



80 



40 



20 



6 



mm. 



mm, 



mm. 



mm. 



mm. 



28-6 



23-8 



, . 



21-8 



419 



27-1 



263 



24-9 



25-0 



49-3 



27-9 



25-1 



24-9 



23-4 



45-6 



With coal-gas there was also a diminution in the deflection 

 when the pressure was diminishad, although here the variations 

 were not so great as in the two previous gases. For this mixture 

 there was obtained the following result : — 



Pressure in the \ 1 atrno- 

 glass cylinder. J sphere. 



Deflections for?" 40*1 

 coal-gas . \ 39-2 - 



Mean . . 39-7 



That the deflections first decrease and afterwards again in- 

 crease when the pressure is diminished, indicates that there are 

 several causes for these variations. The magnitude of the de- 

 flection depends on the electromotive force, on the conducting- 

 power of the spark, and on its duration. That the electromotive 

 force decreases with the pressure follows from the fact that the 

 disintegration of the polar surfaces becomes less as the gas is rare- 

 fied, because the electrical density of the polar surfaces which is re- 

 quisite for the formation of sparks diminishes with the pressure*. 



* In a previous paper I assumed, without any experimental proofs, that 

 the electrical spark is subject to no perceptible change when a voltaic 



