of negative electricity? . 123 



parallel to the axis of the lead cylinder, this cylinder was placed on 

 a levelling table and adjusted so that by altering the level of the 

 table the pencil of y rays could be directed along the axis of either 

 A or B. The vessel containing the cylinders was exhausted to 

 a very high vacuum by Dewar's method of absorption by carbon 

 cooled with liquid air. 



The cylinders were charged (1) positively, (2) negatively, and 

 the rates of leak observed in these cases when the y rays passed (a) 

 through the hollow cylinder,(/3) through the cylinder filled with lead. 

 The leak was small, so that it was necessary to take observations 

 over a considerable time ; from 6 to 30 hours was the time taken in 

 the actual experiments. In this experiment there are two sources 

 of leak, (1) the leak along the quartz support, (2) the leak due 

 to the charges carried by the y and secondary rays. If Z x is the 

 leak when the cylinders are charged positively, l 2 that when they 

 are charged negatively, then the leak along the support is ^ (l x + l 2 ) 

 and that due to the rays |- (l x — 1 2 ). Now let us consider how 

 the leak should differ according as the y rays pass through the 

 hollow cylinder or the one filled with lead. If the charges are 

 carried by the y rays, then since these are absorbed by the lead 

 cylinder and not by the hollow one, the leak due to the rays 

 I (7i — ^2) should be numerically greater when the rays pass through 

 the lead cylinder than through the hollow one ; while if the leak 

 is due to secondary radiation, the leak due to the rays ought to be 

 greater when the rays passed through the hollow cylinder than 

 through the lead one, for the rays give rise to secondary radiation 

 when they come out of the hollow cylinder as well as when they 

 go in, while since the rays are absorbed by the lead there is no 

 secondary radiation at emergence from the solid cylinder. Now 

 it was found in every case that the leak due to the rays was 

 greater when the rays passed through the hollow than when they 

 passed through the solid cylinder, and also that the sign of the 

 leak corresponded to the escape of negative electricity from the 

 cylinder : each of the conclusions is consistent with the view that 

 the effects are due to secondary radiation, and inconsistent with the 

 view that the y rays carry a charge of negative electricity. 



9—3 



