620  Prof.  W.  H.  Bragg  on  the  Ionization  oj 
weights,  so  that  a  simple,  if  approximate,  law  covers  all  the 
phenomena.  It  even  seems  justifiable  now  to  go  one  step 
further.  If  the  list  in  the  paper  quoted  be  examined,  or  the 
more  comprehensive  list  in  Table  A.  it  will  be  found  that  the 
Table  A. 
Table  of  Stopping-powers 
of  various 
Gases. 
Experimental 
Proportional 
Proportional 
"118  s  ',r 
Gas. 
value. 
Air  =  1. 
to  \  :: . 
Air  -  1. 
to  w. 
Air  =  1. 
+-003XW. 
H2  
•243 
■264 
'0695 
•242 
0o   
1-055 
1054 
111 
104 
\\0    
1-46 
1-52 
1-53 
1-49 
CO. 
1-47 
1-51 
1-53 
1-48 
OS  
2-1S 
1-95 
2-71 
1-96 
02H2  
1-11 
117 
•905 
113 
C,H4  
]  -35 
1-44 
•975 
1-37 
C6H6  
3-37 
3-53 
2-71 
339 
C5H]2 
3-59 
3-86 
2-50 
3-66 
CH3Br    ... 
2-09 
203 
3-28 
2-11 
CH3I 
2-58 
2-35 
490 
2-52 
C.H.C1  ... 
236 
2-31 
2-23 
2-30 
C-HJ 
3-13 
306 
5-40 
320 
CHC1,    ... 
312 
2-95 
3-81 
300 
GH10O  ... 
3-40 
3-67 
2-57 
3-51 
CC1 
4-02 
3-59 
5-41 
3-68 
Table  B. 
Table  of  Stopping-powers  of  various  Metal 
Experimental 
Proportional 
Eatio  of  two 
Aletal. 
value. 
to  \  w. 
preceding 
Air  =  1. 
Air  =  1. 
columns. 
Al  
1-45 
1-37 
1-06 
Ye  
2-26 
2-46 
1-97 
2-20 
115 
112 
Ni  
!  Cu 
243 
2-10 
1-16 
!  Ag 
3-17 
274 
1-16 
Sn  
3-37 
2  88 
1-17 
Pt  
416 
3  68 
113 
An 
4-45 
3-7" 
1-20 
Pb  
4-27 
3"i  8 
1-13 
The  last  column  of  Table  A  shows  the  application  of  the  formula  a  s/w  +  hv:  : 
the  agreement  with  the  second  column  is  very  close,  considering  that  only  two 
constants  are  used,  and  one  of  these  is  of  little  importance  except  in  the  case  of 
the  heavier  atoms.  But  the  formula  does  not  appear  to  apply  to  the  metals 
where  the  stopping-power  varies  very  nearly  as  the  square  root  of  the  atomic 
weight.     This  is  certainly  a  difficulty. 
