J. E. Moore — Electrical Discharge, etc. 21 



Art. II. — Electrical Discharge from the point of view of 

 the Kinetic Theory of Matter ; by J. E. Moore.* 



Part I. — On the Nature of Discharge Streams. 



§ 1. Introductory Remarks. 



It is proposed in the present paper to consider some notions 

 concerning the elementary nature of electrical discharge in 

 gases, which are almost wholly dependent upon the kinetic 

 theory of matter. 



However, before beginning, I wish to state that, as these 

 notions are not in all respects in complete agreement with con- 

 clusions reached by some of the Continental and English 

 physicists, I desire to bring them forward with considerable 

 reserve, and with the greatest deference to the opinions of 

 those eminent physicists, who having, perhaps, worked under 

 different conditions, look upon these matters somewhat dif- 

 ferently. 



In order that these notions may be presented in their more 

 general relation to phenomena, other than those of electrical 

 discharge in gases, it is desirable to review briefly some well 

 known facts. 



In the first place it may be mentioned that the physical 

 state of a body of gas is completely defined when we know, 

 for that gas, its (internal) energy, entropy, volume (of a defi- 

 nite mass of the gas), pressure, and temperature. Three of 

 these thermodynamic variables can be, and properly are, 

 regarded as dependent upon the other two. So that the phys- 

 ical state of a body of gas is said to depend only upon its tem- 

 perature and pressure. 



If it be possible to consider electrical discharge through a 

 gas as a function of the thermodynamic variables of that gas 

 it must necessarily follow, that the phenomena of electrical 

 discharge will be found to be dependent only on the tempera- 

 ture and pressure of the gas ; or, since in almost all electrical 

 experiments the temperature is kept constant, for this func- 

 tional relation to exist, electrical discharge phenomena must be 

 found to be dependent only on the pressure (or the molecular 

 density) of the gas. This, as is well known, is actually the case. 

 So that if we place a pair of electrodes in such a gas as air, at 

 atmospheric pressure, discharge can only take place between 

 them disruptively ; and, as the pressure of the gas is made to 

 vary continuously, the phenomena of electrical discharge are 

 seen to vary continuously from disruptive discharge at atmos- 



* Part I presented to the Faculty of Princeton University for the degree of 

 Doctor of Science, June, 1898. 



