546 Prof. A. S. Mackenzie on the Deflexion of 



see that the mass of the a particle is 2*2 times that of 

 the hydrogen atom, or about that of the hydrogen molecule. 

 If helium is monatomic its atomic weight must be 4, and the 

 above experiments do not lend any weight to the view that 

 the a particle is either a hydrogen or a helium atom, but 

 suggest that it is a hydrogen molecule. Even if we take the 



extreme value of — in one direction, viz., 3*7 x 10 5 , and an 



e 



9 



IIXV 



extreme value of in the opposite direction, let us even 



suppose that the dispersion in the electric experiment were 

 great enough to extend to 10 per cent, on either side of the 



9 

 m 71-' 



mean and that could be as small as 37 x 10 14 , the 



e 



calculated mass would be only 3*7 times that of a hydrogen 



atom. A still greater dispersion would be necessary in the 



electric experiment if we were to take the extremes in the 



reverse way in order to bring the mass equal to that of a 



hydrogen atom. It maybe that there are both hydrogen and 



helium sent out together from the radium, and that their 



energies are about the same to give a small electric dispersion, 



but their momenta not nearly so approximately equal. Such 



a condition might give the phenomena observed. 



Magnetic Deflexion of a Hays from Polonium. 



On account of the much feebler a radiation from polonium 

 than from radium, the dimensions of the apparatus for 

 measuring the magnetic and electrostatic deflexions of a. rays 

 from polonium have to be smaller than those used in the 

 experiments already described. The polonium plate, P in 

 figure 5, was obtained from Sthamer of Hamburg, and was 

 in the form of a strip 7 mm. wide and 4 cm. long. It was 

 inserted in the centre of a narrow brass box carrying two 

 tubes opposite to each other and perpendicular to the surface 

 of the plate with the polonium coating ; one of these tubes 

 was connected to the pump, and the other served for holding- 

 inside it the slit-tube, and outside it the brass tube connecting 

 the narrow polonium box with the camera-end E. The slits 

 were about \ mm. wide, and 2*15 cm. apart, and one was in 

 contact with the polonium. The distance from the polonium 

 to the zinc sulphide was 7*33 cm. The whole arrangement, 

 with the exception of the camera-box, could be put between 

 the poles of the electromagnet, shown by the dotted circle in 

 the figure, so that with the exception of the last 5 mm. at 



