386 RECENT PROGEESS IN PHYSICS. 



This opinion is sustained by the fact that the intensity of the spark 

 is very considerably increased if polished brass balls be exchanged for 

 such as have their surface amalgamated, where evidently the trans- 

 ference is greatly facilitated. 



The spark, with the carbon used for Bunsen's battery, is very white 

 in the middle, reddish at the edges, and looks a little like a flame. 



§ 94. Nature of electrical light. — There are two hypotheses as to the 

 nature of the electrical spark ; the first regards it as a motion which 

 is communicated to the ether by the electrical spark ; according to the 

 second hypothesis, electrical light is produced by incandescent pon- 

 derable matter transported by the electricity. 



Masson inclines to the first hypothesis, with which also his experi- 

 ments coincide, since the intensity of the spark depends in no respect 

 upon the fusibility or oxidibility of the balls, but upon their tenacity. 

 If, in consequence of the lower tenacity of the metals, more particles 

 are carried off, the facility of the circuit for conduction is increased ; 

 hence the same quantity of electricity is discharged in a shorter time, 

 whereby a more brilliant light is produced. All of the laws of the 

 brightness of electrical light just mentioned are comprised by the 

 following formula : 



J=:Hf4 (1) 



in which 



J denotes the intensity of the spark ; 



X the striking distance ; 



s the surface of the condenser ; 



Y the distance of the spark from the rotating disk of the photometer ; 



e the thickness of the condenser, and H a constant factor depending 



upon elements which are not yet determined. 



q 



Substituting in equation (1), X=^-^, which is allowable, smce 



s 



Kiess has shown that the striking distance is proportional to the elec- 

 trical density (§ 31), we have 



J=.%.4^ (2) 



Y 



6' 



H»2 

 by making = w, that is, equal to a constant factor which is ad- 

 missible so long as the thickness e of the condenser does not vary. 



q 2 

 Hence the intensity of the electrical light is proportional to -V- the 



square of the electrical density, or which is the same, to the tension 

 of the electricity and the surface s of the condenser. 

 Equation (1) may also be written 



J=Y^X5X 



Substituting for the last X its value ^— , we get 



J=I^Xg. ' (3) 



