12 



L. G. Raub 



is noted that in the great majority of instances the observed vahies 

 at this point are lower than those calculated. 



In Table II are given the observed and calculated potentials in 

 helium at a pressure of 1.55 mm., with a graphical representation 

 in Fig. 5. The results show a reasonably good agreement except 



_U_I I \ I I I I 



.30 



Fig. 5 



.yo <c/77. 



for one reading in the next to the highest current density. 



DETERMINATION OF MOBILITY OF POSITIVE IONS 



The theoretical formula may also be used to determine values of 

 mobility of the positive ions, U , of the gas in the discharge tube. 



