Air in Closed Vessels and its C 



aUSeS. 



559 



Summary of Observations. 





Initial 

 ling. 



Final 

 Beading. 



Change 

 of Zero. 



Deflexion. ' 



Without 



32 

 22-3 

 23-2 



72-7 

 723 

 (53-7 



1-5 



64 



0-4 



Mean ... 



39-2 

 436 

 40-1 



410 



With Wooden 



Screen . 



27- L 

 25-0 



224 



751 



726 



67 3 



30 

 26 



04 



Mean ... 



450 

 450 

 446 



449 



Increase due to Screen, 8*5 per cent. 



It seemed probable that this increase was due to some 

 radiation from the wood, and so the effect of interposing a 

 thin lead >creen between the wood and the instrument was 

 tried. The apparatus was surrounded with a screen of sheet- 

 lead about 2 mm. thick, and the ionization carefully measured. 

 The wooden blocks were now piled up outside the screen, and 

 the ionization was once more measured. The measurement 

 without the wooden blocks was now repeated, and it was 

 found that the wood no longer produced any appreciable 

 effect. Screens of iron and paper were also tried, two thick- 

 nesses of iron being used. The first screen consisted of a 

 ea>t-iron box about I cm. thick, which completely surrounded 

 the apparatus. The results obtained with it are summarized 

 in the following table : — 





Initial 



Reading. 



Final 

 Reading. 



Zero 

 Change. 



Deflexion. 



Without 



9-8 



54-4 



1-3 



459 



Screen. 



14-4 



65*5 



60 



45-1 





211 



67'5 



0-5 



459 





22-7 



716 



22 



51*5 





22-g 



69-2 



67 



Mean ... 



53-0 

 48-3 



With . 



11-2 





3*] 



412 



Screen. 



20-2 



702 



3-6 



46-4 





L9-6 



68-1 



;;■:; 



Mean ... 



45-2 



443 



Diminution due to Screen. N-n per cent. 



