382 



Dr. Willows and Mr. Peck on the Action 



only o£ rays issued, it was possible to investigate the effect at 

 different points of the discharge. The lead case was closed 

 by a thick lid of lead, working on a hinge, which could be 

 opened or closed by the observer at a distance. 



The discharge had the form shown in C, fig. 2. The two 

 sets of numbers given below will show the results and the 

 order of accuracy obtained. 





Near positive 

 knob. 



Middle of discharge. 



Near negative 

 knob. 



Per cent, decrease | 

 of current. ) 



52 



50-5 



45*5 

 41 



33 



30 



Distance of radium, 20 cms. 



The numbers are the mean of a large number of separate 

 observations. It is seen therefore that the positive end is 

 the most sensitive under these conditions. With shorter 

 discharges, the currents were too irregular to admit of 

 conclusions being drawn. 



A reference to 0, fig. 2, shows that the discharge near the 

 anode is concentrated into a single branch very narrow in 

 section. It hence seems probable that the most sensitive 

 part is where the electric field is greatest. We found it 

 impossible to measure this field at different points of the gap. 



Fiff. 3 



The apparatus shown in fig. 3 was used to investigate the 

 effect of altering the pressure of the gas in which the discharge 

 took place. The bell- jar A was 25 cms. long and 12 cms. in 

 diameter. One end was closed with a brass plate, B, through 

 which passed a rubber bung ; D was connected with a water- 

 pump and gauge. The radium capsule, 0, was fastened to 

 a piece of soft iron which allowed of it being shifted to any 



