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Med.  and  Surg.  Jour.,  vol.  clxv,  No.  15,  Oct.  12,  191 1. 
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1902..  iv,  367. 
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40  East  Forty-first  Street. 
MODERN  VIEWS  OX  THE  CONSTITUTION  OF  THE 
ATOM.1 
By  A.  S.  Eve,  D.Sc,  Macdonald  Professor  of  Physics,  McGill  University, 
Montreal.2 
Introduction. 
The  view  that  matter  is  composed  of  discrete  entities,  called 
atoms,  which  are  indivisible,  is  one  of  great  antiquity.  It  was, 
however,  merely  a  speculative  opinion,  not  based  on  experimental 
evidence. 
At  the  present  day  we  can  affirm  that  atoms  have  a  real  existence, 
using  the  word  "  real  "  in  the  ordinary  sense ;  for  instance,  as  a 
bullet  or  stone  may  be  considered  real.  Moreover,  it  is  possible  to 
perform  a  number  of  experiments  which  indicate  clearly  that  atoms 
are  themselves  composed  of  smaller  entities,  termed  electrons,  and  it  is 
not  difficult  to  obtain  some  conception  of  the  number  and  distribution 
and  motion  of  these  electrons  within  the  atom.  Furthermore,  radio- 
active elements,  such  as  radium  or  thorium,  consist  of  atoms  in  a 
state  of  disintegration  or  devolution,  and  it  has  been  possible  to 
detect  single  electrons  projected'  from  radio-active  matter,  and  also 
to  ascertain  that  a  radium  atom  may  eject  the  large  nucleus  of  the 
smaller  helium  atom.  These  remarkable  expulsions  from  the  inner 
citadels  of  certain  atoms  take  place  independently  of  their  physical 
surroundings,  such  as  extremes  of  pressure  and  temperature.  It  is 
noteworthy,  however,  that  the  manner  in  which  these  heavy  atoms 
such  as  uranium  and  radium  are  built  up  from  their  smaller  con- 
stituents, remains  a  profound  mystery. 
1  Based  on  a  lecture  delivered  at  the  meeting  of  the  Section  of  Physics 
and  Chemistry  of  The  Franklin  Institute  held  Thursday,  December  3,  1914. 
2  Reprinted  from  Jour.  Franklin  Institute,  1915,  p.  269. 
