320 ILLINOIS STATE ACADEMY OF SCIENCE 



DEMONSTEATION OF THE WIND IN THE 

 COKONA DISCHARGE 



Jakob Kunz, University of Illinois 



The characteristic pressure increase observed in the 

 corona discharge can be explained by the assumption 

 that the positive ions arising from the luminous layer 

 surrounding the positive wire transmit their momentum 

 to the gas molecules, according to the principle: ne E 

 dt^dp2nr.* It was found that the mobility of the posi- 

 tive ions in various gases is remarkably low, and there- 

 fore the pressure increase rather high, amounting in 

 several experiments to 2 and 3 cm. of water. If the 

 corona discharge takes place in an open gas between 

 parallel wires, then we observe the mechanical momen- 

 tum as a wind away from the positive wire, whereas in 

 a closed cylinder the wind makes itself felt as pressure 

 increase. 



The experimental arrangement was very simple. Two 

 wires of 0.12 mm. diameter, 30 cm. long, and 3 cm. apart, 

 were stretched between two hard rubber plates and a 

 potential difference Avas applied from volts up to 

 18000 volts from a battery of dynamo machines. In a 

 wash bottle was put a small quantity of ether, so that 

 no bubbles were formed by the slow stream of air which 

 was driven through the bottle, carrying ether vapors 

 with it. This stream of air and ether vapor passed 

 through a stop cock, a glass sphere of 10 cm. diameter, 

 and escaped through a capillary of about 1 mm. opening 

 into the air between the parallel wires, forming a beauti- 

 ful regular jet of arbitrary length. This jet between the 

 wires was projected by means of an arc without lenses 

 on a screen. The distance between the arc and the wires 

 was about 1.5 m., and this was also the distance between 

 the wires and the screen. 



When a potential difference of 15000 volts was applied 

 no deflection of the jet could be observed; there was, 

 however, a small deflection for a potential difference a 



* On the Pressure in the Corona Discharge. Phys. Rev., Vol. 19, p. 

 165. 1922. 



