Ami£ch,imipQ"}  Life-History  of  a  Doctrine.  121 
Irom  a  doctrine.  A  law  once  discovered  does  not  wither  and  die. 
It  is  eternal.  Such  a  statement  cannot  be  proved  to  be  true.  It 
calls  for  faith,  but  faith  is  called  for  at  every  turn  in  scientific  mat- 
ters as  well  as  in  spiritual.  Without  it  progress  would  be  impos- 
sible. As  I  am  trying  to  deal  with  doctrines  and  not  with  laws,  let 
me  say  that  doctrines  call  lor  even  a  larger  faith  than  laws.  The 
very  essence  of  a  doctrine  is  faith  in  things  unseen.  The  discovery 
of  the  laws  of  definite  and  multiple  proportions  led  to  the  thought 
of  atoms — not  the  evasive  atoms  of  the  Greeks,  but  atoms  that 
could,  in  a  way,  be  made  the  subject  of  experiment — the  Daltonian 
atoms.  This  conception  appeals  to  some  minds  very  strongly.  It 
is  not  necessary  that  we  should  know  what  the  atoms  look  like, 
though  this  is  highly  desirable.  The  atom  of  chemistry  can  accom- 
plish the  purpose  for  which  it  was  conceived  by  Dalton  by  simply 
standing  for  a  unit  of  matter  that  can  pass  unchanged,  so  far  as  mass 
is  concerned,  through  a  series  of  chemical  changes.  That  is  all  we 
need  to  think  of  under  ordinary  circumstances.  Some  refined 
thinkers  have  found  mental  objections  to  the  atom  and  it  has  been 
the  subject  of  innumerable  attacks.  It  doesn't  do  some  things  that 
it  appears  to  us  it  ought  to  do  and  we  try  to  depose  it  from  time  to 
time.  Particles  that  cannot  be  more  than  o  ooi  of  the  size  of  an 
atom  challenge  the  right  of  the  latter  to  supremacy,  and  the  novelty- 
seekers,  the  born  iconoclasts,  cry  out,  "  Make  way  for  the  corpuscle; 
the  atom  has  had  its  day."  But,  seriously,  the  corpuscle  does  not 
seem  to  threaten  the  atom  of  to-day  or  of  the  immediate  fuiure — ■ 
say  any  time  within  the  next  million  years.  The  atom  may  be 
composed  of  corpuscles.  Indeed,  I  think  chemists  would  rejoice  to 
learn  that  this  is  the  fact.  On  this  point,  let  me  quote  J.  J.  Thom- 
son, the  father  of  the  new  corpuscle.  Speaking  of  Lenard's  observa- 
tion that  the  penetrating  power  ot  the  corpuscles  depends  only  on 
their  density,  he  says :  "  This  is  exactly  what  would  happen  if  the 
atoms  of  the  chemical  elements  were  aggregations  of  a  large  num- 
ber of  equal  particles  of  equal  mass,  the  mass  of  an  atom  being  pro- 
portional to  the  number  of  these  particles  contained  in  it,  and  the 
atom  being  a  collection  of  such  particles  through  the  interstices 
between  which  the  corpuscle  might  find  its  way."  Since  the  density 
depends  only  on  the  number  of  particles  in  unit  volume  and  is  inde- 
pendent of  the  nature  of  the  resulting  atoms,  Lenard's  result  is  a 
strong  confirmation  of  the  view  that  the  atoms  of  the  elementary 
