104 



Mr. A. S. Eve on the Radioactive 



out-of-doors, and for this purpose a large hollow zinc cylinder 

 was used, 610 cms. long and 77 cms. in diameter, having a 

 volume of 2*8 cubic metres, or about one-seventh of that of 

 the large iron water-tank. This cylinder was placed on the 

 College Campus, at some distance from the Physics Building. 

 The active deposit was collected as before on a negatively- 

 charged wire along the axis of the cylinder. When the ends 

 of the cylinder were left open, the amount of observed activity 

 showed the usual variations, and was affected by the velocity 

 of the wind, humidity, and the atmospheric conditions. 

 When the ends were closed, fairly steady results were 

 obtained. 



A comparison of the results is given in the following- 

 table : — 



Table II. 





Total activity in 

 scale-divisions. 



Activity per cubic metre 

 in scale-divisions. 



Zinc cylinder out-of-doors : 



( 1 ) Ends open 



•34 

 •15 



•50 



3-6 



•12 

 •054 



•18 



•19 



(2) Ends closed 



Zinc cylinder in the Engineering- 

 Building 



Iron tank in the 'Engineering 

 Building .- 





The ratio of the volumes of the tank to the cylinder is 

 6*7 : 1, and the ratio of the activities is 24 : 1, so that the 

 excited activity collected in a vessel out-of-doors was between 

 one-third and one-quarter of that collected within the closed 

 tank in the Engineering Building. In order to see whether the 

 effect was apparent or real, the wire cylinder was put in the 

 Engineering Building, not far from the water-tank, and 

 the excited activity was then exactly proportional to that 

 obtained in the large tank. No satisfactory explanation of 

 the difference between the values in the building and out- 

 of-doors has at present been found, and the point will receive 

 further investigation. Radioactive matter has not been 

 introduced into the Engineering Building, and 

 shown later that the rate of production of ions, q, 

 as any observed. 



If we take the values obtained in the cylinder out-of-doors, 

 we must reduce the estimate of the radium bromide required 

 to supply the emanation, in a shell 10 kilometres high over 

 the land-surface of the earth, from 610 to 170 tons. 



it will be 

 was as low 



