80 



Proceedings of Indiana Academy of Science 



Experiments conducted by Francis E. Nipher' show that this luminous 

 column terminates on the plate and becomes longer or shorter depend- 

 ing upon the distance of the plate from the positive needle. 



A 5 mm. hole was made in the center of the zinc plate to see if 

 the corona would pass through this hole to the other needle. It was 

 found that if enough sparks had taken place to ionize the gas sufficiently, 

 the discharge would pass through the hole. By blowing nitrogen in 

 one end of the apparatus, through the hole, and out the other end it 

 was possible to obtain a unidirectional discharge as shown in figure 5. 

 Here the luminous discharge follows the flow of gas through the hole. 

 The positive brush from the W needle is unable to form against the 

 stream of ionized gas flowing through the hole. 



During previous work with alternating current discharges it was 

 noted that an insulated plate placed between needle points appeared 



Fig. 5. Discharge in nitrogen passinc 

 tional effect. 



through hole in zinc plate. Note unidirec- 



to pick up a positive charge as small brushes of positive corona would 

 form on the edges of the plate when a spark occurred between the 

 needles and the plate. In order to determine the nature and amount 

 of this charge the zinc plate was connected so that it might either be 

 grounded through a galvanometer or connected to an electroscope as 

 shown in figure 1. With this arrangement the charge on the plate 

 is determined by the electroscope and any diff'erence in the postive and 

 negative discharge current when the plate is grounded is measured by 

 the galvanometer. Some difficulty was experienced in getting an electro- 

 scope of sufficient range to read all voltages on the plate with any 

 degree of accuracy. 



Two sets of tests were made with each gas, one to determine the 

 effect of voltage on the plate current and potential when the gas is 

 fresh and the other to determine the time effect of discharge with an 



* Experimental Studies in Electricity and Magnetism, Blakiston's Sons Co., Phila- 

 delphia, 1914, p. 3. 



