17(i     Prof.  McCoy  on  the  Relation  between  Radioactivity 
this,  it  can  easily  be  shown,  from  calculations  based  on  the 
numbers  given  in  my  last  paper  on  the  retardation  of  velocity 
of  the  a.  particles  in  their  passage  through  air,  that  the 
decrease  of  curvature  of  the  outside  trace  more  than  com- 
pensates for  the  increase  of  curvature  of  the  inside  trace. 
The  net  result  of  these  two  opposing  processes  is  to  increase 
the  radius  of  curvature  of  the  path,  deduced  from  measure- 
ments on  both  edges  of  the  trace,  to  about  the  extent  observed 
by  M.  Becquerel. 
Summary  of  Results. 
The  following  points  have  been  brought  out  in  this  paper: — 
(1)  The  rays  from  radium  in  radioactive  equilibrium  are 
complex   and    consist  of   «   particles   projected    with 
different  velocities. 
(2)  The  a  particles  decrease  in  velocity  in  their  passage 
through,  air  and  through  aluminium. 
(3)  The  absence  of  increased  deflexion  of  the  rays  from  a 
thick  layer  of  radium  after  passing  through  alu- 
minium, observed  by  M.  Becquerel,  is  a  necessary 
consequence  of  the  complexity  of  the  rays, 
(4)  The  decreasing  curvature  of  the  path  of  the  rays  in 
air,  observed  by  M.  Becquerel,  is  also  a  necessary 
consequence  of  the  complexity  of  the  rays. 
(5)  There  is  evidence  of  a  distinct  scattering  of  the  rays 
from  radium  C  in  their  passage  through  air. 
A  full  discussion  of  the  connexion  between  the  ionizing, 
phosphorescent,  and  photographic  actions  of  the  a,  rays  will 
be  reserved  for  a  later  paper. 
Macdonald  Physics  Building-, 
McGiil  University,  Montreal,  Nov.  15,  1905. 
XIV.  The  Relation  between  the  Radioactivity  and  the  Compo- 
sition of  Uranium  Compounds.  By  Herbert  X.  McCoy, 
Asst.  Prof  of  Chemistry,  University  of  Chicago  *. 
rilHE  early  determinations  f  of  the  radioactivity  of  pure 
I  uranium  compounds  showed  but  a  roughly  approximate 
proportionality  between  the  activity  and  the  percentage  of 
uranium.  The  methods  used  did  not  take  into  account  the 
absorption  of  the  alpha  rays,  to   which  ionization  is  almost 
*  Communicated  bv  the  Author.  Read  before  the  Amer.  Phys.  Soc, 
Chicago,  April  21,  1905 ;  Abstract,  Phys.  Rev.  xx.  p.  381  (1905). 
t  Mme.  Curie,  These,  Paris,  1903 ;  also  Chem.  News,  lxxxviii.  p.  98 
(1903).    McCoy,  Ber.  d.  Chem.  Ges.  xxxvii.  p.  2641  (1904). 
