1!)03.] Effect of Extreme Cold on the Emanations of Radium. 69 



" Note on the Effect of Extreme Cold on the Emanations of 

 Radium." By Sir WILLIAM CROOKES, F.R.S., and Professor 

 JAMES DEWAB, F.RS. Received and read May 28, 1903. 



As it seemed advisable to examine the action of extreme cold on 

 the action of radium, the following experiments have been made, in 

 continuation of work formerly done by either of us separately. 



The first endeavour was to ascertain whether the scintillations 

 produced by radium on a sensitive blende screen were affected by 

 cold. 



A small screen of blende with a morsel of radium salt close in front 

 was sealed in a glass tube, and a lens was adjusted in front so that 

 the scintillations could be seen. On dipping the whole into liquid air 

 they grew fainter and soon stopped altogether. Some doubt was felt 

 whether this might not have been caused (1) by the presence of liquid, 

 (2) by the screen losing sensitiveness, or (3) by the radium ceasing to 

 emit the heavy positive ions. To test this two tubes were made, in 

 one of which the radium salt could be cooled without the screen, and 

 in the other the screen could be cooled while the radium salt was at 

 the ordinary temperature. The accompanying sketch explains their 

 construction. 



Fml. 



Cold 

 RaduiTti. 



FIG. 2. 



Cold 

 Screen. 



'GLciss Window. 

 Lofiu 

 Screen. 



\ Rcidium. 



^Lx3.ss Window. 

 Screen. 



VOL. LXXII. 



