17(5 



PROFESSOR E. RUTHERFORD ON THE 



of an electrometer. The gold-leaf system was insulated inside <>t' a metal vessel by 

 means of a sulphur bead, after the method first employed by C. T. K. WILSON 



Fig. 3. 



(see fig. 3). The rate of movement of the leaves was determined through mica 

 windows by means of a microscope provided with a micrometer eye-piece. For 



100 



E Exposure (i min^Dej 



60 



30 40 50 



Time in Minutes. 



Fig. 4. 



measurements with the ft rays, the active rod was placed under the electroscope, and. 

 before entering into the vessel, passed through a sheet of metal of sufficient thickness 



