774.  Prof.  J.  J.  Thomson  on  the 
The  value  of  the  logarithmic  term  is  somewhat  uncertain, 
involving  as  it  does  the  indeterminate  quantity  a  ;  it  cannot, 
however,  be  large  enough  to  alter  the  order  of  the  term  on 
the  right-hand  side.     If  M/  is  the  mass  of  the  hydrogen  atom, 
—  —  1 04  • 
M'  * 
hence  we  have 
M  1*4 
n  = 
i.  e.,  n  is  of  the  same  order  as  M/M'  the  atomic  weight  of  the 
element. 
Thus  these  three  very  different  methods  all  lead  to  the  result 
that  the  number  of  corpuscles  in  the  atom  of  an  element  is 
of  the  same  order  as  the  atomic  weight  of  the  element  ;  and 
from  the  first  method  we  conclude  that  the  mass  of  the 
carrier  of  unit  positive  charge  is  large  compared  with  that  of 
the  carrier  of  unit  negative  charge.  If  we  suppose  the  whole 
mass  of  an  atom  to  be  that  of  its  charged  parts,  e/m  for  positive 
unit  charge  would  be  of  the  order  104. 
An  obvious  argument  against  the  number  of  corpuscles  in 
the  atom  being  as  small  as  these  results  indicate,  is  that  the 
number  of  lines  showing  the  Zeeman  effect,  which  must 
therefore  be  due  to  the  vibrations  of  corpuscles,  in  the 
spectrum,  say,  of  iron  is  very  much  greater  than  the  atomic 
weight  of  iron.  This  objection  would  be  conclusive  if  it 
could  be  shown  that  all  these  lines  are  due  to  the  vibrations 
of  eorpuscles  inside  the  normal  atom  of  iron ;  but  I  submit 
that  there  is  no  evidence  that  this  is  the  case.  When  an  atom 
of  an  element  is  giving  out  its  spectrum  either  in  a  flame  or 
in  an  electric  discharge,  it  is  surrounded  by  a  swarm  of 
corpuscles;  and  combinations,  not  permanent  indeed,  but 
lasting  sufficiently  long  for  the  emission  of  a  large  number 
of  vibrations,  might  be  expected  to  be  formed.  These  systems 
would  give  out  characteristic  spectrum-lines;  but  these  lines 
would  be  due,  not  to  the  vibrations  of  corpuscles  inside  the 
atom,  but  of  corpuscles  vibrating  in  the  field  of  force  outside 
the  atom.  Such  lines  would  not  be  reversed  by  cold  vapour, 
though  they  might  be  by  very  hot  vapours,  by  the  vapours 
in  flames  or  in  the  neighbourhood  of  an  electric  discharge  : 
the  number  of  lines  showing  the  Zeeman  effect  reversed  by 
cold  vapours  is,  however,  very  limited. 
We  shall  now  proceed  to  consider  the  theory  of  the  method 
on  which  the  preceding  results  are  based. 
