﻿Chemistry 
  and 
  Physics. 
  235 
  

  

  than 
  at 
  the 
  other, 
  thus 
  affecting 
  the 
  total 
  amount 
  of 
  radiation 
  

   falling 
  on 
  the 
  retina. 
  Also, 
  if 
  such 
  an 
  objection 
  were 
  valid, 
  it 
  

   would 
  imply 
  that 
  fatigue 
  of 
  the 
  muscles 
  of 
  the 
  iris 
  produced 
  a 
  

   relatively 
  enormous 
  'time-lag' 
  in 
  following 
  changes 
  of 
  lumi- 
  

   nous 
  intensity, 
  which 
  we 
  know 
  does 
  not 
  exist. 
  

  

  There 
  seems, 
  in 
  fact, 
  to 
  be 
  little 
  doubt 
  that 
  the 
  difference 
  is 
  due 
  

   to 
  the 
  retina 
  itself 
  becoming 
  sensitive 
  to 
  long 
  waves 
  after 
  rest, 
  

   which 
  were 
  incapable 
  of 
  affecting 
  it 
  when 
  it 
  was 
  in 
  some 
  way 
  

   fatigued 
  by 
  exposure 
  to 
  the 
  ordinary 
  bright 
  light 
  of 
  day. 
  

  

  The 
  next 
  and 
  obvious 
  step 
  is 
  to 
  find 
  the 
  respective 
  wave-lengths 
  

   corresponding 
  to 
  the 
  different 
  temperatures. 
  This 
  point, 
  how- 
  

   ever, 
  and 
  others, 
  cannot 
  be 
  determined 
  without 
  some 
  additions 
  to 
  

   the 
  present 
  apparatus, 
  and 
  will 
  form 
  the 
  subject 
  of 
  a 
  future 
  paper." 
  

   — 
  Proc. 
  Phys. 
  Soc, 
  London, 
  xiii, 
  122. 
  

  

  8. 
  On 
  the 
  liquefaction 
  of 
  air. 
  — 
  A 
  note 
  communicated 
  by 
  

   Professor 
  George 
  Davidson. 
  The 
  recent 
  remarkable 
  experi- 
  

   ments 
  of 
  Professor 
  Dewar 
  in 
  liquefying 
  air, 
  etc., 
  recall 
  the 
  

   experiments 
  of 
  Perkins 
  in 
  1822-1826 
  as 
  detailed 
  in 
  a 
  paper 
  of 
  the 
  

   Royal 
  Society 
  read 
  June 
  15, 
  1826 
  (p. 
  541). 
  

  

  Mr. 
  Perkins 
  describes 
  the 
  apparatus 
  which 
  he 
  had 
  devised 
  and 
  

   operated 
  ; 
  and 
  says, 
  " 
  this 
  tube 
  [of 
  steel] 
  I 
  filled 
  with 
  water 
  and 
  

   subjected 
  it 
  to 
  a 
  pressure 
  of 
  2,000 
  atmospheres. 
  After 
  repeating 
  

   this 
  experiment 
  a 
  great 
  number 
  of 
  times, 
  the 
  average 
  of 
  the 
  result 
  

   showed 
  that 
  the 
  column 
  of 
  water, 
  8 
  inches 
  long, 
  was 
  compressed 
  

   § 
  of 
  an 
  inch, 
  or 
  y 
  1 
  ^ 
  part 
  of 
  its 
  length." 
  

  

  "With 
  the 
  same 
  apparatus 
  I 
  also 
  made 
  experiments 
  on 
  the 
  

   compression 
  of 
  other 
  fluids. 
  The 
  most 
  remarkable 
  result 
  I 
  ob- 
  

   tained 
  was 
  with 
  concentrated 
  acetic 
  acid; 
  which, 
  after 
  com- 
  

   pression 
  with 
  a 
  force 
  of 
  1100 
  atmospheres, 
  was 
  found 
  to 
  be 
  

   beautifully 
  crystallized, 
  with 
  the 
  exception 
  of 
  about 
  T 
  V 
  part 
  of 
  

   fluid, 
  which, 
  when 
  poured 
  out, 
  was 
  only 
  slightly 
  acid 
  

  

  As 
  it 
  might 
  be 
  supposed 
  that 
  even 
  glass 
  was 
  pervious 
  to 
  water 
  

   by 
  such 
  a 
  force, 
  [500 
  atmospheres,] 
  a 
  small 
  phial 
  was 
  made 
  air- 
  

   tight, 
  by 
  fitting 
  into 
  its 
  neck 
  a 
  well-ground 
  glass 
  stopper. 
  It 
  

   sustained 
  pressure 
  of 
  500 
  atmospheres 
  without 
  change 
  and 
  was 
  

   perfectly 
  dry 
  within, 
  although 
  it 
  remained 
  under 
  that 
  pressure 
  15 
  

   minutes. 
  It 
  was 
  next 
  subjected 
  to 
  a 
  pressure 
  of 
  800 
  atmospheres, 
  

   and 
  when 
  taken 
  out 
  was 
  found 
  to 
  be 
  crushed 
  to 
  atoms. 
  

  

  " 
  In 
  the 
  course 
  of 
  my 
  experiments 
  on 
  the 
  compression 
  of 
  atmos- 
  

   pheric 
  air, 
  by 
  the 
  same 
  apparatus 
  that 
  had 
  been 
  used 
  for 
  com- 
  

   pressing 
  water, 
  I 
  observed 
  a 
  curious 
  fact, 
  which 
  induced 
  me 
  to 
  

   extend 
  the 
  experiment 
  ; 
  viz., 
  that 
  of 
  the 
  air 
  beginning 
  to 
  disappear 
  

   at 
  a 
  pressure 
  of 
  500 
  atmospheres, 
  evidently 
  by 
  partial 
  liquefaction, 
  

   which 
  is 
  indicated 
  by 
  the 
  quicksilver 
  not 
  settling 
  down 
  to 
  a 
  level 
  

   with 
  its 
  surface. 
  At 
  an 
  increased 
  pressure 
  of 
  600 
  atmospheres, 
  

   the 
  quicksilver 
  was 
  suspended 
  about 
  -J 
  of 
  the 
  volume 
  up 
  the 
  tube 
  

   or 
  gasometer 
  ; 
  at 
  800 
  atmospheres, 
  it 
  remained 
  about 
  J 
  up 
  the 
  

   tube; 
  at 
  1000 
  atmospheres, 
  §- 
  up 
  the 
  tube, 
  and 
  small 
  globules 
  of 
  

   liquid 
  began 
  to 
  form 
  about 
  the 
  top 
  of 
  it; 
  at 
  1200 
  atmospheres, 
  the 
  

   quicksilver 
  remained 
  £ 
  up 
  the 
  tube, 
  and 
  a 
  beautiful 
  transparent 
  

  

  