188 Messrs. E. Marsden and H. Eichardson on the 



of great importance in many experiments in which these 

 substances have been used in experiments on a particles. 

 The alteration of air-equivalent tends to diminish for high 

 ranges in all cases, although there is no indication of the 

 values becoming constant *. 



Table II. 





Gold. 



i 





Aluminium. 



Emergent 

 Range. 





1 























A. 



E 



•7 







C. 



A. 



B. 



C. 



00 



•299 



50 





1-310 



•769 



•918 



1-344 



05 



•384 



•895 





1-487 



•820 



1-015 



1-422 



10 



•426 



•972 





1-613 



•851 



1-051 



1-473 



1-5 



•452 



1-021 





1-681 



•869 



1073 



1-499 



2-0 



•471 



1066 





1-733 



•880 



1-086 



1-514 



3 



•502 



1-118 





1-822 



•888 



. 1102 



1-525 



40 



•522 



1-161 





1-899 



•892 



1110 



1-528 



50 



•533 



1-195 







•895 



1116 



1-530 



6-0 



•547 

















Mica. 



Copper. 



Silver. 



Tin. 



Platinum. 



Emergent 

 Range. 











' 















i 









A. 



B. 







A. 



B. 







00 



•536 



•875 



•668 





•750 



1-650 



1-451 



2-968 



05 



•601 



•937 



•787 





•831 



1-775 



1-561 



3-198 



10 



•623 



•964 



•860 





•874 



1-851 



1-618 



3-353 



1-5 



•631 



•977 



•896 





•900 



1-902 



1-655 



3460 



20 



•636 



•984 



•916 





•922 



1-9-10 



1-681 



3544 



3-0 



•647 



•990 



•939 





•953 



2-000 



1-725 





4-0 



•655 



•995 



•956 





•977 



2054 



1-760 



... 



50 



•663 



1000 



•972 





1000 







• ■ • 



60 















... 



... 



The question arises as to what is the quantity which we 

 have called air-equivalent. As we are measuring in all 

 cases the end of the range of the particles which have not 

 been appreciably deflected from their path, scattering can 

 have little influence on the results. A factor which might 

 come in is the phenomenon which Darwin has f termed 

 "straggling." Darwin states, "In traversing matter some 



no © ' © 



a particles encounter more atoms than others and go deeper 

 into them. Thus after going a given distance the a particles 

 will have straggled out and some will be moving faster than 



* Cf. Bragg, 'Studies in Radioactivity,' p. 52. 



t C. G, Darwin, Phil, Mag. vol. xxiii. p. 901 (1912). 



