Prof. Norton on Molecular Physics. 107 



along this line. This result will be partially due to the lateral 

 expansion which the free electricity received by the air-particles 

 on the line will occasion in their electric atmospheres. There 

 will be two causes in operation to produce this effect — the pres- 

 sure of the stream of sether passing from one particle to the next, 

 against the atmosphere upon which it falls, and the mutual repul- 

 sion of the particles that will thus become momentarily over- 

 charged. We have seen (p. 105) that such lateral expansion 

 would give rise to a diminution in the resisting force of the pola- 

 rized molecules. 



As the positive electricity which thus passes over to b spreads 

 over its surface, it partially neutralizes its negative state, and 

 thus tends to check the flow and interrupt the passage of the 

 spark. There is also a sudden diminution in the tension of the 

 electricity received by a from the prime conductor, which is another 

 cause of this interruption. Apparently another cause conspi- 

 ring with these two is a reaction to the sudden lateral expansion 

 above mentioned. If a were previously charged and insulated 

 and b brought continually nearer to it, the mutual inductive 

 action of the two balls upon each other would initiate the elec- 

 tric movement above alluded to through the intervening air, 

 which would finally result in the passage of a spark. 



The light of the spark results in part from the vibratory 

 movements in the atmospheres of the air-molecules attendant 

 upon the discharge. (See p. 430.) Experiments by Riess, Mas- 

 son, and other physicists have conclusively established that the 

 electric light is partially due to the passage of highly luminous 

 metallic particles from the positive to the negative surface. The 

 detachment of such particles, as one result of the discharge, may 

 be explained by the discharges, or flow, of electricity that must 

 take place directly through the ball a when the conductive dis- 

 charge from a to b occurs. This follows from the fact that the 

 electricity within the ball is no longer in equilibrium under the 

 action of the electrical shell that surrounds it, and the impulses 

 conveyed by the electric current should tend to detach the par- 

 ticles at the end of the metallic line through the ball. The 

 luminosity of the detached particles is to be ascribed to the 

 vibratory movements imparted by the discharge to the electric 

 atmospheres of the particles. 



Excitation of 'Electricity : — There are various special modes of 

 exciting electricity ■ but they are all only so many different modes 

 of polarizing contiguous molecules, or, more comprehensively, 

 of effecting certain disturbances in the equilibrium of electric 

 atmospheres. The different special causes of disturbance in 

 these cases may all be traced to some action of the molecular 



