﻿478 
  Transactions, 
  — 
  Chemistry, 
  

  

  movement, 
  it 
  occurred 
  to 
  me 
  to 
  try 
  camphor 
  itself. 
  I 
  placed 
  a 
  large 
  piece 
  of 
  

   it 
  upon 
  water 
  in 
  a 
  vessel 
  closed 
  from 
  tlie 
  air, 
  and 
  found, 
  after 
  the 
  lapse 
  of 
  

   about 
  four 
  hours, 
  that 
  it 
  was 
  stationary, 
  and 
  that 
  fresh 
  pieces 
  put 
  therein 
  

   would 
  not 
  move. 
  I 
  then 
  took 
  out 
  the 
  camphor 
  and 
  exposed 
  the 
  water 
  

   freely 
  to 
  the 
  air 
  for 
  a 
  short 
  time, 
  when 
  I 
  found 
  that 
  camphor 
  would 
  then 
  

   describe 
  very 
  lively 
  movements 
  upon 
  it. 
  The 
  same 
  kind 
  of 
  effects 
  are 
  not 
  

   produced 
  if 
  the 
  camphor 
  is 
  kept 
  wholly 
  immersed 
  in 
  the 
  water, 
  not 
  even 
  if 
  

   the 
  time 
  of 
  contact 
  is 
  prolonged 
  to 
  a 
  week. 
  I 
  further 
  found 
  that 
  a 
  water^ 
  

   surface, 
  which 
  has 
  been 
  rendered 
  unfavourable 
  for 
  these 
  movements 
  by 
  

   camphor, 
  is 
  also 
  in 
  a 
  very 
  unfavourable 
  condition 
  for 
  the 
  spread 
  of 
  oils 
  

   thereon, 
  so 
  much 
  so 
  that 
  some 
  of 
  them, 
  when 
  so 
  placed, 
  that 
  is, 
  of 
  course, 
  

   when 
  used 
  in 
  small 
  quantity, 
  keep 
  nearly 
  to 
  the 
  drop 
  form. 
  

  

  The 
  very 
  pertinent 
  facts 
  are, 
  then, 
  now 
  distinctly 
  shown, 
  that 
  many 
  

   vapours 
  are 
  obstructive 
  to 
  camphoric 
  movements 
  when 
  condensed 
  within 
  or 
  

   upon 
  the 
  upper 
  stratum 
  of 
  any 
  water 
  on 
  which 
  camphor 
  is 
  moving, 
  and 
  

   that 
  among 
  these 
  substances 
  is 
  camphor 
  itself. 
  Now 
  we 
  have 
  already 
  seen 
  

   that 
  all 
  the 
  substances 
  just 
  named 
  above 
  (and 
  this 
  includes 
  camjyhor) 
  are 
  

   capable 
  under 
  certain 
  circumstances 
  of 
  giving 
  very 
  decided 
  and 
  rapid 
  move- 
  

   ments 
  to 
  solid 
  particles 
  when 
  they 
  occupy 
  a 
  water-surface 
  ; 
  and 
  we 
  have 
  

   also 
  seen 
  that 
  these 
  vapours 
  do 
  not 
  effect 
  this 
  directly 
  by 
  what 
  I 
  may 
  here 
  

   designate 
  vaj)our 
  force, 
  but 
  rather 
  by 
  surface 
  modification. 
  The 
  conclusion, 
  

   therefore, 
  which 
  one 
  is 
  led 
  to 
  by 
  a 
  consideration 
  of 
  all 
  this 
  is, 
  that 
  the 
  

   movements 
  of 
  camphor 
  in 
  question 
  are 
  the 
  effect 
  of 
  surface 
  modification 
  and 
  

   modiflcatiun 
  ivJiich 
  it 
  -produces 
  itself. 
  

  

  The 
  analogy 
  is, 
  I 
  hold, 
  complete 
  between 
  resin 
  upon 
  water 
  moving 
  away 
  

   from 
  that 
  which 
  has 
  been 
  modified 
  by 
  vapour, 
  and 
  camphor 
  upon 
  water 
  

   moving 
  away 
  from 
  the 
  water 
  it 
  has 
  modified, 
  except 
  that 
  we 
  have 
  one 
  sub- 
  

   stance 
  less 
  in 
  the 
  latter 
  than 
  in 
  the 
  former 
  case 
  — 
  thus, 
  camphor 
  placed 
  

   upon 
  water 
  gives 
  up 
  a 
  part 
  of 
  its 
  substance 
  to 
  the 
  upper 
  stratum 
  thereof; 
  

   this 
  part 
  represents 
  the 
  vapours, 
  whether 
  of 
  alcohol, 
  ether, 
  or 
  camphor, 
  

   which 
  are 
  resident 
  in 
  the 
  clearing 
  they 
  have 
  made 
  amongst 
  the 
  particles 
  of 
  

   resin 
  with 
  which 
  the 
  water 
  has 
  been 
  laden 
  ; 
  the 
  remaining 
  part 
  of 
  the 
  

   camphor 
  represents 
  the 
  resin 
  which 
  has 
  been 
  removed 
  to 
  make 
  this 
  clearing. 
  

  

  Such 
  is 
  the 
  theory 
  which 
  I 
  submit 
  to 
  you 
  as 
  explanatory 
  of 
  the 
  pheno- 
  

   mena 
  we 
  have 
  been 
  observing. 
  I 
  think 
  you 
  will 
  readily 
  allow 
  that 
  it 
  is 
  at 
  all 
  

   events 
  the 
  most 
  probable 
  of 
  any 
  which 
  you 
  have 
  now 
  had 
  for 
  this 
  purpose, 
  

   and 
  now 
  it 
  only 
  remains 
  for 
  me 
  to 
  state 
  to 
  you 
  what 
  I 
  conceive 
  to 
  be 
  — 
  

  

  1. 
  The 
  precise 
  nature 
  of 
  the 
  surface 
  modification 
  which 
  I 
  have 
  

  

  credited 
  camphor 
  with 
  producing. 
  

  

  2. 
  The 
  manner 
  in 
  which 
  a 
  surface 
  so 
  modified 
  forces 
  camphor 
  to 
  

  

  move. 
  

  

  