554 



Prof. 



J. J. Thomson on the Masses of 



d (in cm.). 



H. 



V in absolute 

 measure. 



e/m. 



•18 



170 



40 X 10 s 



8-5 x 10" 



•19 



170 



30 X 10 s 



5-8 X 10 s 



■20 



181 



46 x10 s 



7-0 x 10 s 



•29 



167 



84 x10 s 



71 x 10 6 



•29 



164 



90x10* 



7-6xl0 G 



•30 



160 



86 x10 s 



7-4 Xl0 6 



•45 



100 



80 x10 s 



7-9 x 10 s 



giving a mean value for e/m equal to 7*3 X 10 6 . The value I 

 found for e/m for the cathode rays was 5xl0 6 ; the value 

 found by Lenard was 6*4 x 10 6 . Thus the value of e/m in 

 the case of the convection of electricity under the influence 

 of ultra-violet light is of the same order as in the case of the 

 cathode rays, and is very different from the value of e/m in 

 the case of the hydrogen ions iu ordinary electrolysis when 

 it is equal to 10 4 . As the measurements of e, the charge 

 carried by the ions produced by ultra-violet light to be 

 described below, show that it is the same as e for the hydrogen 

 ion in electrolyis, it follows that the mass of the carrier in the 

 case of the convection of negative electricity under the influence 

 of ultra-violet light is only of the order of 1/1000 of that of 

 the hydrogen atom. Thus with ultra-violet light, as with 

 cathode rays, the negative electrification at low pressures is 

 found associated with masses which are exceedingly small 

 fractions of the smallest mass hitherto known — that of the 

 hydrogen atom. 



1 have examined another case in which we have convection 

 of electricity at low pressures by means of negatively electrified 

 particles — that of the discharge of electricity produced by an 

 incandescent carbon filament in an atmosphere of hydrogen. 

 In this case, as Elster and Geitel (Wied. Ann. xxxviii. p. 27) 

 have shown, we have negative ions produced in the neigh- 

 bourhood of the filament, and the charge on a positively 

 electrified body in the neighbourhood of the filament is dis- 

 charged by these ions, while if the body is negatively electrified 

 it is not discharged. If the filament is negatively, and a 

 neighbouring body positively electrified, there will be a 

 current of electricity between the filament and the body, 

 while there will be no leak if the filament is positively and 

 the body negatively electrified. Elster and Geitel (Wied. 



