68o INDUSTRIAL APPLICATIONS. 



1240. ELECTROSTATIC MACHINES. In apparatus for producing 

 statical electricity, as in frictional or multiplying machines (194), 

 the motion produces a continuous transport of electricity between 

 the two conductors which join the collectors or the poles of the 

 machine. If the poles are connected by a conductor, the action 

 of the machine maintains a continuous current in the conductor, 

 and the difference of potential of the poles is feeble. If the inter- 

 mediate conductor is connected by a spark discharger, a series of 

 discharges is produced, and the difference of potential of the poles 

 increases periodically and disappears at each spark. In all cases 

 the efficiency of the machine is the quantity of electricity which 

 flows in unit time. 



The striking distance, which increases with the difference of 

 potential, is only limited by the dimensions of the parts and the 

 distance of the collectors. 



The quantity of electricity produced is almost independent of 

 the striking distance, so long as this is small compared with the 

 greatest striking distance that is to say, a few millimetres in or- 

 dinary machines but it then diminishes rather rapidly. Other 

 things being equal, the quantity is proportional to the velocity of 

 rotation, or, more exactly, to the extent of surface of the plates or 

 cylinders which are utilised by the comb in unit time. The ratio 

 of the quantity to the surface utilised appears greater for reaction 

 machines than for frictional machines, and varies notably with the 

 nature of the glass. 



It is interesting to estimate the quantity of work transformed 

 into electricity in an electrostatic machine. A Holtz machine with 

 two rotating plates 60 cm. in diameter* was used to charge a battery, 

 the electrostatic capacity of which was 225 metres or 22,500 (C.G.S.) 

 that is to say, in practical units (613), 



225. io 2 . r , 



= 0-025. i o~ 15 , or 0-025 microfarads. 

 3 2 . io 20 



With seven turns of the machine, the charge of the battery was 

 sufficient to produce a spark of 0*1 cm. in a discharger the balls of 

 which were 2*2 cm. in diameter, which corresponds to a difference 

 of potential (822) of 5,490 volts. 



MASCART. Traite d" 1 Electricitt Statiqtte, Vol. II., p. 324. 



