128 



W. Duane — Effect of a Magnetic Field 



millimeter, and the electric force is not much greater than 10 

 volts per centimeter, magnetic fields of over 1000 gauss dimin- 

 ish the positive current in air very perceptibly. With an elec- 

 tric force of 25 volts per centimeter, however, no effect is 

 produced by the magnetic field up to 2600 gauss, apart from 

 the initial drop. 



In hydrogen the effect is much more pronounced than in air, 

 and takes place also under larger electric forces. 



The fact that in air no effect except the initial drop is pro- 

 duced by the magnetic field, if the electric force is greater 

 than 25 volts, or the pressure greater than 0*03 mm , proves that 

 the diminution of the current absorbed at low pressures and 

 for smaller electric and large magnetic forces can not be 

 due to the suppression of (3- or secondary rays, and must be 

 due to the deflection of the ions. 



The adjoining tables contain the currents measured in a 

 number of experiments : 



Negative Currents. Electric Force = 25 volts cm. 



Magnetic 

 Field. 



30 mm 



15 mm 



gmm 



^mm 



^ •zj.inm 



•28mm 



•06 mir - 







•666 



•555 



•910 



•955 



2-80 



•42 



•0503 



324 



__ 











•870 



2-33 



•058 



•0024 



56V 



•625 



•513 



•800 



•835 



1-27 



•0159 





1107 



•572 



•450 



•645 



•392 



•274 



•0040 



__ 



1593 



•513 



•370 



•392 



•182 



•079 







1989 



•476 



•280 



•230 



•091 



•026 



•0022 





2600 



•426 



•169 



•097 



•029 



•012 



-- 



-- 



The first column contains the magnetic field expressed in 

 gauss ; and the others the rate at which the potential of the 

 electrode changes expressed in volts per second, this rate being 

 proportional to the ionization current. At the head of each 

 column appears the corresponding pressure of the gas in the 

 ionization chamber, and (for the positive currents) the electric 

 force in volts per centimeter. 



The columns are not comparable with each other, for widely 

 different quantities of emanation were used in the different 

 experiments. In order to present more clearly the way in 

 which the currents decrease with increasing magnetic fields, 

 the curves in figs. 3 and 4 have been drawn, taking in each 

 case the current for zero fields as 100. 



