602 



On the' a Particles of Radium. 



pass the ionization chamber by a distance x measured in air, 

 and those from the lowest by a distance x — d, d being the 

 effective thickness of the layer measured in air. When x is 

 less than d 7 as in the top part of the ionization curve, the 

 ionization is proportional to 



(^ + 6- ) 2 ^+ 2) -5 2/(n + 2) . 



I find that when n is put equal to 1, d being estimated at 

 •5 cm., s = 2*37 cm., when n = 2, s =I'33 cm., and when 

 ?i = 3, s = '8 cm.: and I have calculated a few values on the 

 ionization curves given by the above formulae for each of these 

 values of n. I have placed alongside some corresponding 

 actual observations, making all the curves nearly agree at a 

 distance 6*4 cm. from the Ra. 



1 

 I 

 j Distance 



Calculated Values of Ionization. 





from 

 i Radium. 



! 







Observed 



91=1. 



»=2. 



n=S. 



Values. 



! 7-0 



















6-8 



132 



120 



116 



115 



6-4 



282 



277 



283 



273 



6-0 



266 



248 



237 



250 



5-5 



252 



223 



200 



21.8 



5-0 



242 



205 



176 



200 



45 



233 



191 



157 



187 



4-0 



224 



1 177 



144 



177 



3-5 



217 



168 



133 



172 



So far, therefore, as the evidence goes, it is now in favour 

 of the value n = 2. It is interesting to observe that when one 

 particle flies at great speed past another which is relatively 

 at rest, the energy given by the ionizing to the stationary 

 particle, in consequence of their mutual attractions or repul- 

 sions, is inversely proportional to the square of the velocity 

 of the moving particle. (Report of the Australasian Asso- 

 ciation for the Advancement of Science, Dunedin, 1904, 

 p. 64.) 



I am, Gentlemen, 



Yours faithfully, 



W. 11. Bragg. 



