132 W. Duane— Effect of a Magnetic Field. 



around 2000 gauss, if the electric force is 10 volts. Substitu- 

 ting the values in equation (1), putting d —1, we have 



ejm — 500. 



The ratio e/m for the nitrogen and oxygen atoms and molecules 

 are approximately 700, 612, 350 and 306, and it follows, there- 

 fore, that a large number of the positive ions in air must have 

 masses of the order of magnitude of those of the nitrogen and 

 oxygen atoms and molecules. 



The magnetic field suppresses a much larger proportion of 

 the positive current in hydrogen than in air even when the 

 electric force is 25 volts per centimeter, which proves that in 

 hydrogen the ratio e/m for a large number of positive ions 

 must be much greater than 700, and unless the charge is very 

 large, the mass of these ions must be much less than that of 

 the nitrogen atom. 



The facts that the drop in the current is not sharply defined 

 and the positive current not completely suppressed may be 

 due to the presence of ions of different masses, or it may be 

 because the initial velocity of the ions is not negligible or that 

 their mean free paths are not long enough. Further experi- 

 ments with larger electric and magnetic forces, and perhaps at 

 very low temperatures (to reduce the velocity of the molecules), 

 may elucidate these points. 



