[     503     ] 
LXII.  Reply  to  "An  Examination  of  the  recent  attack  on  the 
Atomic  Theory:'     By  C.  R.  A.  Wright,  D.Sc.  Lond.* 
WHEN  there  is  a  difference  of  opinion  about  matters  of 
fact,  it  is  usually  traceable  to  the  use  of  the  same  words 
in  different  senses  j  wherefore  it  is  always  advisable  to  preface 
a  discussion  by  strictly  defining  the  particular  meanings  attached 
to  the  words  employed.  Mr.  R.  W.  Atkinson  refers  to  my 
paper  "On  the  Relations  between  the  Atomic  Hypothesis  and 
the  Condensed  Symbolic  Expressions  of  Chemical  Facts  and 
Changes  (Dissected  Formulae)"  as  an  attack  on  the  Atomic  Theory; 
but  the  terms  atomic  hypothesis  (as  I  employ  it)  and  atomic 
theory  (as  the  latter  is  employed  in  University  College  Labora- 
tory) mean  two  utterly  different  things — so  much  so,  that  Dr. 
Williamson,  in  his  admirable  essay  "On  the  Atomic  Theory" 
(Chem.  Soc.  Journ.  1869,  p.  3.28),  denies  that  notions  which  I 
have  understood  as  necessarily  involved  in  the  atomic  hypothesis 
are  essential  to  the  atomic  theory.  For  instance, he  exemplifies  the 
meaning  of  the  term  "atom"  thus  (p.  364): — "In  potassic  hydrate 
oxygen  is  combined  with  hydrogen ;  it  is  also  combined  with 
potassium ;  but  the  hydrogen  cannot  pass  off  even  at  a  red  heat 
in  combination  with  its  half  of  the  oxygen.  The  two  halves  are 
inseparable ;  and  when  I  say  that  in  a  molecule  of  potassic  hy- 
drate there  is  a  single  atom  of  oxygen,  I  merely  express  that 
fact ; "  in  other  words,  Dr.  "Williamson  uses  the  term  atom  in 
this  instance  to  express  on\y  facts  which  are  otherwise  expres- 
sible thus  :  "  the  radical  0  is  bivalent  in  reaction  where  the 
substance  designated  by  the  formula  KOH  is  concerned;  and 
this  substance,  unlike  the  analogous  thallous  hydrate,  T10H, 
does  not  undergo  a  reaction  such  as  that  indicated  by  the  sym- 
bols 2KOH  =  HOH  +  KOK  by  the  action  of  heat."  Later 
on,  Dr.  Williamson  refers  to  atoms  thus  (p.  365): — "The  ques- 
tion as  to  whether  our  elementary  atoms  are  in  their  nature 
indivisible,  or  whether  they  are  built  up  of  smaller  particles,  is 
one  upon  which  I,  as  a  chemist,  have  no  hold  whatever;  and  I 
may  say  that  in  chemistry  the  question  is  not  raised  by  any  evi- 
dence whatever.  They  may  be  vortices  such  as  Thomson  has 
spoken  of;  they  may  be  little  hard  indivisible  particles  of  regular  or 
irregular  form."  And  again  (Discussion,  p.  434),  "  Whether  the 
smallest  particles  of  matter  have  a  spherical  form  or  not,  whether 
they  are  in  their  nature  indivisible,  whether  they  are  in  reality 
the  ultimate  atoms  of  matter,  or  like  the  planets  of  this  system, 
he  knew  not,  nor  did  such  questions  exist  for  him  as  a  chemist. 
He  therefore  thought  it  wise  to  exclude  them,  important  as  they 
were,  from  the  existing  atomic  theory." 
*  Communicated  by  the  Author. 
