HIGH VOLTAGE — COMPTON 



255 



electrostatic generator. 'J'he action of this generator consisted in 

 Mowing drops of condensed steam, by the steam pressure, out through 

 a series of nozzles against a neighboring metal plate. The droplets 

 of water were charged by frictional contact against the walls of the 

 nozzles. The electrical power was created by the work done in 

 moving the charged droplets against the electric field which devel- 

 oped between the nozzle and the plate on whicli the droplets struck, 

 and, of course, this power was in turn derived from the driving 

 power of the steam, which carried the dr()j)lets out and away from 

 the nozzle. 



Another whole series of electrostatic generators was built upon the 

 principle of electrostatic induction. Perhaps the simplest of these 

 was the Belli doubler, which was devised in 1831 and operated on the 

 same principle as a later 

 device designed by Lord 

 Kelvin and better known 

 as tlie " Kelvin replen- 

 isher ", described by him 

 in 1872. This action is 

 shown schematicall}'^ in 

 figure 1. When the rotat- 

 ing member with the in- 

 sulated plates E and F is 

 at the position shown, 

 positive and negative 

 c barges are separated 

 from the connecting wire, 

 w h i c h brushes lightly 

 against E and F, by means 



of the electrostatic forces arising from the charges on the neighbor- 

 ing metal armatures C and D. As the rotating arm turns and breaks 

 contact with these brushes the charges are carried on E and F and, 

 when they touch the springs C and Z>, respectively, these charges are 

 communicated to the armatures, thus increasing the charge already 

 existing on these armatures. Then at the next contact with the 

 brushes at E and F the process is repeated. Consequently the charge 

 on the armatures continually builds up until it reaches such magni- 

 tude, or rather until the voltage rises so high that the charge leaks 

 away as fast as it is produced, leaking away either through the insula- 

 tion or by a corona discharge produced by breakdown of the 

 surrounding air. 



A large variety of instruments, some simple and some very compli- 

 cated, have been developed to carry on the idea of the Belli doubler 

 in a more efficient manner. Such instruments were devised by Varley 

 in 1860, by Toepler in 1865, and by Holtz between 1864 and 1880, but 



;ci!E 1 



hematic dincriim of Kolvin roplenislu-r. 



