produced by ft Particles from Radioactive Substances. Gil 



of the table, which are the figures referring to the more 

 penetrating radiation. It will be noticed that the figures 

 (column 7) for Act C, Th D, and Ra B are nearly the same, 

 and those for RaE and UrX are again similar, but different 

 from the above; for Ra C the figure is unique. 



Several suggestions may be offered to account for the 

 variations, and we intend to discuss the following possible 

 explanations : — 



(1) The differences might be attributed to a variation of 

 the ionizing power of the ft particles of different speed. 



(2) The differences might be ascribed to an erroneous 

 calculation of the number of atoms breaking due to the 

 presence of unknown a-ray products. 



(3) The high values might be due to the presence of /3-ray 

 products not yet known, or to the simultaneous emission of 

 two ft particles from the disintegrating atom. 



As to the first point, a comparison of the absorption co- 

 efficients with the figures given for the ionization (column 7) 

 shows that this supposition cannot account for the differences; 

 ActC and Th D both having fairly hard radiations and Ra B 

 with a much softer radiation give about the same value. On 

 the other hand, UrX emitting a radiation similar to Th D, 

 and Ra E which is much softer, give a value approximately 

 half that of the first-named substances. This indicates that 

 a change in ionization with velocity cannot explain the 

 differences. 



The second point raised above might at first appear plausible 

 on account of the fact that the values for Ur X and Ra E come 

 out about half of the values of Th D, ActC, and RaB. If 

 radium itself and polonium give off two a particles instead of 

 one, as assumed, the figures for UrX and RaE would be 

 double, and come into some agreement with the other products. 

 However, investigations by other observers give no indi- 

 cation whatever in favour of this hypothesis. 



It appears to be more likely that the third suggestion is 

 the correct explanation, although we are well aware of certain 

 difficulties which arise. It appears necessary to assume that 

 ActC, Th D, and RaB, and perhaps also Ra C, emit two ft 

 particles, or consist of two successive products each emitting 

 ft rays. The recent experiments of v. Baeyer, Hahn, and 

 Meitner * on the deflexion of the ft rays from the active 

 deposit of thorium can perhaps be brought forward in support 

 of our view, and perhaps also the measurements of Makower f, 

 on the charge carried by the /3 rays from the active deposit of 



*' v. Baeyer, Hahn, and Meitner, Phys Zeits. xii. p. 273 (1911). 

 t W. Makower, Phil. Mag. xvii. p. l71 (1909). 



