378 A. W. Eivell — Air in an Intense Electric Field. 



10~ 18 for e ; 1*55 for v, whicli is Cbattock's value for the mean 

 velocity of the ions in the point discharge at atmospheric pres- 

 sure, under unit intensity ;* and 3-J3-. 10~ 3 for i, the current per 

 square centimeter ; n, the number of ions per cubic centimeter 

 comes out 1.3 * 10 10 . Taking the number of molecules per 

 cubic centimeter as 2.4* 10 19 , the proportional ionization of the 

 molecules is 2.7 ■ 10- 10 .t 



The effect of temperature and. the displacement current 

 before ionization begins are illustrated in fig. 6. Both elec- 

 trodes were 30 cm X 30 cm . No guard ring was used because 

 the insulated guard ring made it difficult to maintain a uniform 

 temperature different from that of the room, and the area of 

 the inner portion was too small to enable the displacement 

 current to be measured with the apparatus at my disposal. 

 The curves are therefore uncorrected. The temperature within 

 this range has evidently little influence except upon the 

 dielectric constant. The dotted line gives the calculated 

 displacement current (equation (3) ). 



An alternating e.m.f. has been employed throughout for 

 reasons explained at the beginning. The character of the 

 e.m.f. could not, however, qualitatively affect the main 

 results, and therefore, for air at ordinary temperature and 

 pressure, as the current carried through the air by ions 

 increases, the required electromotive force slowly increases to 

 a maximum and then decreases, and tends to become inde- 

 pendent of the thickness of air. Moreover, for alternating 

 electromotive forces of approximately sine form, quantitative 

 results have been obtained which make possible the calculation 

 of Siemens ozonizers. 



I wish to express my thanks to Prof. Harold B. Smith for 

 the use of the high potential apparatus of the Department of 

 Electrical Engineering. 



Worcester Polytechnic Institute, September, 1906. 



* Thomson, Conductivity of Elec. through Gases, p. 56. 



f Compare the data given in Winkelmann, vol. IV, 2d ed., p. 561. 



