642 PROCEEDINGS OP THE AMERICAN ACADEMY. 



Since it is supposed that there is not only a negative particle e shot 

 out from the negative terminal, but also a positive particle c' shot out 

 from the positive terminal, we have similar expressions for u u v x , w x , for 

 the velocity of the positive particle. 



Professor Thomson analyzes thus the equations for u, v, w. The 

 first term in the numerator represents a velocity parallel and propor- 

 tional to the electric force ; the second term, a velocity at right angles 

 both to the electric and magnetic forces. The third term represents 

 a velocity parallel to the magnetic force. The relative importance of 

 these terms depends upon the value of R H. If this quantity is small 

 the first term is the most important, and the ion moves parallel to the 

 electric force ; if, on the other hand, R H is large, the last term is the 

 most important and the ion moves parallel to the magnetic force. As R 

 varies inversely as the pressure of the gas, it might, at very low pres- 

 sures, be possible to make R H large enough and thus make the ions 

 travel along the lines of magnetic force. The same reasoning can 

 doubtless be applied to the movement of the positive particle, and we 

 then have a consideration of the relative rotation effect under the 

 influence of the magnetic field on the two particles, the negative and 

 the positive, and the relative progression effect along the lines of mag- 

 netic force. In the discussion also we must bear in mind the fruitful 

 hypothesis of Townshend in regard to the collision of the ions. 



It may be that the difference in magnetic properties of oxygen and 

 hydrogen contained in the rarefied air also plays an important part in 

 the phenomena which are presented in this paper. I hope to present 

 later the results of a study of the behavior of oxygen and other gases 

 submitted to electric discharges in a magnetic field. The conclusions 

 I draw from these experiments are as follows : — 



1. Strong, steady currents and high differences of potential introduce 

 us to phenomena which are concealed by inadequate currents, low 

 potential differences, and weak magnetic fields. 



2. At definite pressures, where the free path of the molecule is short, 

 the cathode violet light is repelled to the edge of the circular disc forming 

 the cathode by a magnetic field, the lines of which are directed along the 

 line of electric discharge, and revolves with a speed dependent upon the 

 pressure of rarefied air. We have, in this case, a distinct unipolar 

 rotation. Besides the violet light, there is also a rotation of an orange- 

 colored plume-like discharge. 



3. When the anode is made the core of an electro-magnet at high 

 pressures, the discharge is separated into two ; one a violet discharge, 



