UNIVERSITY 



INTRODUCTION 



IN Maxwell's Electricity published in 1873, section 

 57, the following sentence occurs in connection with 

 the discharge of electricity through gases, especially 

 through rarefied gases : 



" These and many other phenomena of elec- 

 trical discharge are exceedingly important, and, 

 when they are better understood, they will 

 probably throw great light on the nature of 

 electricity as well as on the nature of gases and 

 of the medium pervading space." 



This prediction has been amply justified by the 

 progress of science, and, no doubt, still further 

 possibilities of advance lie in the same direction. 

 The study of conduction through liquids, first, and 

 the study of conduction through gases, next, com- 

 bined with a study of the processes involved in 

 radiation, have resulted in an immense addition to 

 our knowledge of late years, and have opened a new 

 chapter, indeed a new volume, of Physics. 



The net result has been to concentrate attention 

 upon the phenomena of electric charge, and greatly 



