136 Mr. L. Simons on the Beta-Ray Emission from 



According to the theory outlined in the introduction, the 

 numbers in these six columns, it multiplied by the constant 

 n h, give respectively the energies of the K, L, and M 

 electrons emitted by the various screens when they are 

 subjected first to Apr X-ra^ T s and then to Ba X-rays, the K 

 electrons being the least rapid and the M electrons the most 

 rapid ones. 



This close study by Beatty's "pressure variation" method 

 has led me to the conclusion that it ie extremely difficult to 

 distinguish any variation in the maximum range in the 

 /3-ravs emitted by the various screens all exposed to rays of 

 one type; the practical reason is that the beam of the /3-rays 

 is so attenuated, both by the transfoimation of its energy 

 into ions and by diffusion near iis extreme range, and 

 theoretically from the fact that the numbers in column (c) 

 or in column (/), Table I., are so close together, that the 

 electrons, whose range according to Whiddington's fourth- 

 power law should be proportional to the squares of these 

 numbers, are almost indistinguishable. Or better, the 

 electrons of maximum energy are the peripheral electrons 

 whose potential energy within the parent atom is negligibly 

 small, whatever the atom may be, in comparison with the 

 incident quantum. They emerge with piactically the whole 

 of she energy of the incident quantum, and their range will 

 be almost independent of the nature of the parent atom, as 

 Barkla and Shearer have already shown. Those numbers 

 referring to the ranges which these experiments might be 

 able possibly to distinguish from each other or from the 

 mean maximum range are italicised in Table I. These are 

 taken out in Table II. One further point worth mention is 

 that when Silver X-rays (K) type are incident on silver or 

 on elements just above silver in atomic weight, there is no 

 K emission of X-rays, but groups of electrons possessing a 

 large amount of energy. A similar statement is true for 

 Barium (K) X-rays on barium. This accounts for Sadler's 

 observation. 



The distances in the two columns marked "range 5 ' are 

 obtained from the positions of the minima of the curves 

 in figs. 8 and 9 (PL III.) respectively. According to this 

 work, these are approximately the distances traversed in air 

 at 0° 0. and 76 cm. pressure by the groups of electrons 

 having ranges which could be distinguished bv this method 

 from those of the fastest groups. From Whiddington's 

 fourth-pow T er law, which must be regarded as approximate, it 

 follows that Sljd' should be constant, where E is the kinetic 

 energy of the electrons of range d in air. Apart from the 



