M. I. Pupin — Electrical discharges, etc. 46< 



Art. L1X. — On Electrical Discharges through poor Vacua, 

 and on Coronoidal Discharges ;* by M. I. Pupln, Ph.D., 

 Columbia College. With Plate XIY. 



INTRODUCTION. 



The behavior of electrical discharges through poor vacua 

 does not seem to have received the attention of experimental 

 investigators which it deserves. This may seem strange in 

 view of the uncertainty of our knowledge of the process 

 by which the transfer of electricity through gases takes place. 

 Considering, however, that it was generally customary to 

 employ in experimental investigations of this kind a vacuum 

 jar with metal electrodes in connection with an electric gene- 

 rator of small capacity, it is easily explained why the discharges 

 through poor vacua should have received so much less atten- 

 tion than the discharges through high vacua and the spark 

 discharges through gases at ordinary pressures. Neither the 

 vacuum jar, nor the working of the electric generators ordi- 

 narily employed, admitted of rapid, easily adjustable, but essen- 

 tial variations in the conditions of the experiment; as for 

 instance, variations of the size and shape of the electrode, of 

 the frequency of the discharges, of the strength of the electro- 

 motive force, etc. But, as I shall point out in the course of 

 this paper, it is through these very variations that certain fun- 

 damental features in the character of an electrical discharge 

 through poor vacua are brought out prominently. 



The fact that electrical discharges in poor vacua resemble in 

 many characteristic details the appearance and behavior of 

 the solar corona attaches additional interest and importance to 

 that class of experimental investigations which are pointed out, 

 only, in this paper. Neither time nor facilities permitted me 

 to aim at anything approaching completeness. The principal 

 aim in my presenting this paper was to recommend my subject 

 and my method of investigating it to those who command over 

 a larger experience and skill in experimental investigations, 

 and who also have more leisure and greater experimental facili- 

 ties than I could even pretend to possess. 



DESCRIPTION OF THE EXPERIMENTAL METHOD. 



A brief description of the method by which I obtained my 

 vacuum discharges seems in place now. It consists in produc- 

 ing an electrical current in a vacuum by means of the con- 



*Eead before the National Academy of Sciences, Washington, April 22nd, 1892. 



