144 Prof. E. Rutherford on Uranium Radiation and 



A tube A (fig. 10) was taken, 3 metres long and 5" 5 cm. 

 in diameter. A cylinder D, 25 cm. long, had its interior 

 surface coated with uranium oxide. This cylinder just fitted 

 the large tube, and its position in the tube could be varied 

 by means of strings attached to it, which passed through 

 corks at the ends of the long tube. The air was forced 



•Fiff. 10. 



D __ W& 



Earth 



Earth 



through the tube from a gasometer, and on entering the tube 

 A passed through a plug of cotton-wool, E, in order to remove 

 dust from the air and to make the current of air more 

 uniform over the cross-section of the tube. The air passed 

 by the uranium surface and then through a gauze L into 

 the testing cylinder B of 2*8 cm. diameter. An insulated 

 rod C, 1*6 cm. in diameter, passed centrally through the 

 cylinder B and was connected with the electrometer. The 

 cylinders A and B were connected to one pole of a battery of 

 32 volts, the other pole of which was to earth. 



The potential-difference of 32 volts between B and C was 

 sufficient to almost completely remove all the ions from the 

 gas in their passage along the cylinder. The rate of leak of 

 the electrometer was thus proportional to the number of ions 

 in the gas. 



The following rates of leak were obtained for different 

 distances of the uranium cylinder from the gauze L 

 (table, p. 145). 



The first column of the table gives the distances of the 

 end of the uranium cylinder from the gauze L. d (about 

 20 cm.) was the distance for which the first measurement 

 was made. In the second column the time intervals taken 

 for the air to pass over the various distances are given. The 

 value of t corresponds to the distance d. The mean velocity 

 of the current of air along .the tube was about 25 cm. per sec. 



