478 



Dr. J. L. Glasson on 



columns III. and IV. of Table I. The value for argon is 

 that obtained by Adams (Phys. Rev. vol. xxiv. p. 108, 

 1907). The constancy of the figures in column IV. is a 

 measure of the range and of the success of the rule. 



Table I. 



I. 



II. 



III. 



IV. . 



V, 



VI. 



VII. 





Symbol. 



At. Wt. 



Stopping 

 Power. 





At. No. 



2 



N 3 . 



(7 





H 



1 

 4 



•24 



■43 



240 

 214 



1 

 2 



100 240 

 1-59 ! 





He 













C 



12 

 14 

 14*4 



16 



•85 



•94 



1*00 



P05 



246 

 252 

 264 



9«9 



6 



7 

 7'2 



8 



3-30 

 3-66 

 371 



4-00 



256 

 256 

 269 



262 





N 





Air 



o 









i 





Al 



S 



27 

 32 

 35-5 

 40 



1-49 < 288 

 1-76 312 



1-78 ■ 299 

 1-83 290 



13 

 16 

 17 



18 



5-52 

 6-36 

 6-60 



6-87 



270 

 275 

 270 

 267 





CI 



A 















Fe 



56 

 59 

 64 



80 



229 307 

 2-44 | 319 

 2-46 309 

 2-60 291 



26 8-77 260 





Ni 



28 

 29 

 35 



9-21 1 262 



9-44 I 262 



10-7 242 





Cu 





Br 









As 



108 

 119 

 127 



3-28 ! 315 

 3-56 ' 326 

 3-44 ' 307 



47 

 50 

 53 



130 

 13-6 

 141 



253 

 260 

 244 





Sn 





I 





Pt 





195 

 197 



207 



4-14 ! 297 

 4-22 ! 301 

 4-27 298 



78 

 79 

 82 



18-2 

 18-4 

 18-9 



227 

 228 

 226 • 





Au 





Pb 





| 









2. In fig. 1 the logarithms of the atomic stopping power 

 are plotted against the logarithms of the atomic number. 

 The observed values lie nearly on a straight line whose slope 

 is almost exactly two-thirds. In fig. 1 the line is drawn so 

 as to pass through the air or standard point and have the 

 slope two-thirds. It will be seen that it fits the observations 

 very well. The relation between <r and N is of the form 

 <7 = &lN% where £ = '262 and is the atomic stopping power of 

 hvdro.ien. We may say therefore that " The stopping power 

 •of an atom is proportional to its atomic number raised to the 

 power two-thirds." 



3. It is perhaps desirable to inquire how well this rule 

 fits the observed values and to compare its success with 



