﻿RECENT 
  DISCOVEEIES 
  AND 
  THEOEIES 
  RELATING 
  TO 
  

   THE 
  STRUCTURE 
  OF 
  MATTER. 
  1 
  

  

  By 
  Karl 
  Taylor 
  Compton, 
  

   Professor 
  of 
  Physics 
  in 
  Princeton 
  University. 
  

  

  Molecules 
  of 
  matter 
  are 
  sometimes 
  defined 
  as 
  the 
  smallest 
  sub- 
  

   divisions 
  which 
  have 
  the 
  properties 
  of 
  the 
  matter 
  which 
  they 
  com- 
  

   pose. 
  Their 
  existence 
  has 
  long 
  been 
  accepted 
  because 
  of 
  the 
  satis- 
  

   factory 
  explanation 
  which 
  they 
  give 
  of 
  elastic, 
  thermal, 
  and 
  other 
  

   properties 
  of 
  matter, 
  particularly 
  in 
  the 
  gaseous 
  state. 
  More 
  re- 
  

   cently 
  the 
  existence 
  of 
  such 
  particles 
  in 
  rapid 
  random 
  motion 
  has 
  

   been 
  made 
  almost 
  visible 
  in 
  that 
  we 
  can 
  accurately 
  explain, 
  by 
  the 
  

   bombardment 
  of 
  such 
  molecules, 
  the 
  erratic, 
  jerky 
  movements 
  made 
  

   by 
  a 
  small 
  particle 
  immersed 
  in 
  a 
  gas 
  or 
  liquid 
  and 
  observed 
  through 
  

   a 
  microscope. 
  

  

  Atoms 
  are 
  sometimes 
  defined 
  as 
  the 
  smallest 
  particles 
  which 
  take 
  

   part 
  in 
  chemical 
  reactions, 
  and 
  a 
  chemical 
  reaction 
  is 
  simply 
  a 
  

   change 
  from 
  one 
  to 
  another 
  kind 
  of 
  grouping 
  made 
  by 
  atoms 
  of 
  the 
  

   same 
  or 
  of 
  different 
  kinds. 
  Any 
  characteristic 
  grouping 
  of 
  atoms 
  

   constitutes 
  a 
  molecule. 
  The 
  existence 
  of 
  atoms 
  was 
  first 
  suggested 
  

   to 
  explain 
  the 
  fact 
  of 
  chemical 
  combination 
  of 
  substances 
  in 
  definite 
  

   proportions. 
  

  

  Within 
  the 
  last 
  25 
  years, 
  and 
  chiefly 
  within 
  the 
  last 
  10 
  years, 
  

   definite 
  proof 
  of 
  the 
  existence 
  of 
  atoms 
  and 
  molecules 
  has 
  been 
  found 
  

   and 
  methods 
  have 
  been 
  developed 
  to 
  count 
  and 
  weigh 
  them 
  indi- 
  

   vidually, 
  with 
  very 
  significant 
  results. 
  More 
  important 
  still, 
  it 
  has 
  

   been 
  shown 
  that 
  all 
  atoms 
  are 
  themselves 
  built 
  out 
  of 
  still 
  smaller 
  

   and 
  more 
  fundamental 
  units 
  of 
  matter, 
  electrically 
  charged, 
  called 
  

   positive 
  electrons 
  and 
  negative 
  electrons. 
  There 
  is 
  very 
  decisive 
  

   evidence 
  of 
  the 
  existence 
  of 
  these 
  two 
  fundamental 
  types 
  of 
  matter 
  

   and 
  of 
  the 
  number 
  of 
  each 
  type 
  in 
  any 
  given 
  kind 
  of 
  atom. 
  To 
  this 
  

   extent 
  the 
  " 
  electron 
  theory 
  of 
  matter 
  " 
  is 
  no 
  longer 
  to 
  be 
  considered 
  

  

  1 
  Reprinted 
  by 
  permission 
  from 
  Princeton 
  Lectures, 
  No. 
  10, 
  Princeton 
  University, 
  Prince- 
  

   ton, 
  N. 
  J., 
  June, 
  1922. 
  

  

  145 
  

  

  