330 Mr. T. C. Porter on the 



great importance. It seems certain that we cannot regard 

 the #-rays as having the same relation to /3-rays as cathode- 

 rays have to Rontgen rays which they produce ; for we have 

 shown that the separated active products from uranium and 

 thorium contain all the substance responsible for the /3-rays. 

 The radioactive material, which has thus been temporarily 

 freed from /3-rays, still, however, retains its power of giving 

 out, in the case of uranium a large proportion, and in the case 

 of thorium about 30 per cent, of the original a-rays. 



This a-radiation persists, in the case of uranium, several 

 days, and, in the case of thorium several hours, without any 

 appreciable change in intensity. If the a-rays are due 

 directly to the /3-rays, it is necessary to assume that the radia- 

 tion persists for long intervals after its exciting cause is 

 removed. This view also fails to explain, without additional 

 assumptions, why the radiation from Ur.X. does not excite 

 similar a-radiation s in itself. 



Without, at this stage, going into views on the mechanism 

 of radioactivity, it seems probable that most of the deviable 

 rays from uranium and thorium are given out by a secondary 

 product produced by a disintegration of the uranium or 

 thorium atom or molecule. These secondary products differ 

 in chemical properties from the uranium and thorium, and 

 can be separated from them by chemical means, and thus give 

 rise to Ur.X. and Th.X. The non-de viable radiation may be 

 either due to the other secondary product of the reaction, or 

 may be due to an action of the product responsible for the 

 deviable rays in the mass of the radioactive material. 

 McGill University, Montreal. 

 May 7, 1902. 



XXXV. On the Ebullition of Rotating Water. — A Lecture 

 Experiment. By T. 0. Porter, Eton, Bucks* 



IF the water in a beaker, having approximately vertical 

 sides, be caused to rotate about an axis concentric with 

 the vertical geometrical axis of the beaker, it is obvious that in 

 any horizontal section of the water the pressure is least in the 

 centre, and increases from the centre outwards. It is also a 

 well-known fact that the temperature at which water boils de- 

 pends upon the pressure to which it is subjected, being lower the 

 lower this pressure is. Thus if a beaker of water were at a tem- 

 perature just below the boiling-point, and it could be suddenly 

 made to rotate throughout its mass without cooling it, the water 

 would turn into vapour in and about the axis of least pressure, 

 from the surface downwards, forming, at all events for the 

 * Communicated by the Physical Society : read May 23, 1902. | 



