876 Dr. J. W- Nicholson on a Structural 



should be done in all possible cases. It seems not unlikely 

 that some of the lines of the nebular and coronal spectra 

 would be found, just as helium has been found. 



Some calculations which may be made from the experi- 

 mental results are very significant, and one or two may be 

 cited as illustrations. In the first place, though the methods 

 of finding e/m for the ql rays from radium have been criti- 

 cized, they have led to very concordant results. Rutherford's 

 original investigation by the electric method gave ejm — 6 . 10 3 . 

 The photographic method of Des Coudres gave a value 

 (r4 . 10 3 , and this was confirmed later by Rutherford by a 

 combination of the magnetic deflexion and the heating effect, 

 which gave 6'5 . 10 3 . This agreement is remarkable, and 

 certainly an indication that the results are probably correct. 

 Now the value of ejm for a hydrogen atom with the elec- 

 tronic charge, as in electrolysis, is 9*62 . 10 3 . Taking 



ejm = 6*4 . 10 3 



for the a particle, its mass becomes therefore 15 times that 

 of the hydrogen atom. If it has a double charge, this 

 becomes 3 times that of the hydrogen atom. This does not 

 point to helium as the a particle, but to the gas Nu 2 , which 

 we may call Dinebulium, with an atomic weight 3*25. This 

 may be the origin of the three spectral lines already men- 

 tioned. There is evidence that the a particles from the 

 emanation differ either in mass or velocity from those of 

 radium. Rutherford has concluded that they have a smaller 

 velocity. It is possible, however, that they have a larger 

 mass, and really consist of helium. 



One more calculation of considerable interest may be 

 given. Becquerel has concluded that the amount of devi- 

 ation, in a given magnetic field, is the same for the a rays 

 of polonium and radium. This means that the momentum 

 mV of the rays is the same. But the u rays from polonium 

 are much more readily absorbed, and therefore apj arently 

 m is greater for these rays. In Rutherford's treatise * a 

 comparative table of the absorptions is given. For a single 

 thin layer of aluminium foil, the ratio of decrease is, for 

 polonium, *41, and for radium, '48. Afterwards polonium 

 rays cease to follow the exponential law. In a single thin 

 layer, it cannot be very invalid to suppose the decrease pro- 

 portional roughly to the velocity, or the time which it would 

 take a ray to get through. If, then, the a ray from radium 

 is really dinebulium, that from polonium has an atomic 



* ' Radioactivity/ p. 162, 



