﻿160 
  Lord 
  Rayleigh 
  on 
  the 
  Lubricating 
  

  

  feet 
  of 
  about 
  the 
  same 
  size 
  and 
  shape 
  as 
  the 
  glass 
  ones 
  

   gave 
  different 
  results. 
  It 
  should, 
  however, 
  be 
  noticed 
  that 
  

   the 
  brass 
  feet, 
  though 
  fairly 
  polished, 
  could 
  not 
  have 
  been 
  

   so 
  smooth 
  as 
  the 
  fire 
  surfaces 
  of 
  the 
  glass. 
  The 
  present 
  

   carriage 
  weighed 
  (with 
  its 
  load) 
  6^ 
  oz., 
  and 
  on 
  the 
  well- 
  

   handled 
  glass 
  slide 
  moved 
  with 
  \ 
  oz. 
  in 
  pan. 
  When 
  the 
  

   slide 
  was 
  breathed 
  upon, 
  the 
  motion 
  was 
  as 
  free 
  as, 
  perhaps 
  

   more 
  free 
  than, 
  before. 
  And 
  when 
  the 
  feet 
  stood 
  in 
  a 
  pool 
  

   of 
  water, 
  there 
  was 
  equal 
  freedom. 
  A 
  repetition 
  gave 
  

   confirmatory 
  results. 
  On 
  another 
  da}^ 
  paraffin 
  oil 
  was 
  

   tried. 
  At 
  the 
  beginning 
  J- 
  oz. 
  in 
  pan 
  sufficed 
  on 
  the 
  

   handled 
  slab. 
  With 
  a 
  pool 
  of 
  oil 
  the 
  carriage 
  still 
  moved 
  

   with 
  \ 
  oz.in 
  pan, 
  but 
  perhaps 
  not 
  quite 
  so 
  certainly. 
  As 
  

   the 
  oil 
  was 
  removed 
  with 
  blotting-paper 
  the 
  motion 
  became 
  

   freer, 
  and 
  when 
  the 
  oil-film 
  had 
  visibly 
  disappeared 
  the 
  

   \ 
  oz. 
  in 
  pan 
  could 
  about 
  be 
  dispensed 
  with. 
  Doubtless 
  

   a 
  trace 
  of 
  oil 
  remained. 
  The 
  blotting-paper 
  was 
  of 
  course 
  

   applied 
  to 
  the 
  feet 
  and 
  legs 
  of 
  the 
  carriage, 
  as 
  well 
  as 
  to 
  

   the 
  slab. 
  

  

  In 
  attempting 
  to 
  interpret 
  these 
  results, 
  it 
  is 
  desirable 
  to 
  

   know 
  what 
  sort 
  of 
  thickness 
  to 
  attribute 
  to 
  the 
  greasy 
  films 
  

   on 
  handled 
  surfaces. 
  But 
  this 
  not 
  so 
  easy 
  a 
  matter 
  as 
  when 
  

   films 
  are 
  spread 
  upon 
  water. 
  In 
  an 
  experiment 
  made 
  some 
  

   years 
  ago* 
  I 
  found 
  that 
  the 
  mean 
  thickness 
  of 
  the 
  layer 
  on 
  

   a 
  glass 
  plate, 
  heavily 
  greased 
  with 
  fingers 
  which 
  had 
  touched 
  

   the 
  hair, 
  was 
  about 
  J 
  of 
  the 
  wave-length 
  of 
  visible 
  light, 
  

   viz. 
  about 
  10 
  ~ 
  4 
  mm. 
  The 
  thickness 
  of 
  the 
  layer 
  necessary 
  

   to 
  induce 
  slipperiness 
  must 
  be 
  a 
  small 
  fraction 
  of 
  this, 
  

   possibly 
  T 
  \ 
  T 
  , 
  but 
  perhaps 
  much 
  less. 
  We 
  may 
  compare 
  this 
  

   with 
  the 
  thickness 
  of 
  olive 
  oil 
  required 
  to 
  stop 
  the 
  camphor- 
  

   movements 
  on 
  water, 
  which 
  I 
  found 
  f 
  to 
  be 
  about 
  2 
  X 
  10 
  ~ 
  6 
  mm. 
  

   It 
  may 
  well 
  be 
  that 
  there 
  is 
  little 
  difference 
  in 
  the 
  quantities 
  

   required 
  for 
  the 
  two 
  effects. 
  

  

  In 
  view 
  of 
  the 
  above 
  estimate 
  and 
  of 
  the 
  probability 
  that 
  

   the 
  point 
  at 
  which 
  surface-tension 
  begins 
  to 
  fall 
  corresponds 
  

   to 
  a 
  thickness 
  of 
  a 
  single 
  layer 
  of 
  moleules 
  t, 
  we 
  see 
  that 
  

   the 
  phenomena 
  here 
  in 
  question 
  probably 
  lie 
  outside 
  the 
  

   field 
  of 
  the 
  usual 
  theory 
  of 
  lubrication, 
  where 
  the 
  layer 
  of 
  

   lubricant 
  is 
  assumed 
  to 
  be 
  at 
  least 
  many 
  molecules 
  thick. 
  We 
  

   are 
  rather 
  in 
  the 
  region 
  of 
  incipient 
  seizing, 
  as 
  is 
  perhaps 
  not 
  

   surprising 
  when 
  we 
  consider 
  the 
  smallness 
  of 
  the 
  surfaces 
  

  

  * 
  Phil. 
  Mag. 
  vol. 
  xix. 
  p. 
  96 
  (1910) 
  ; 
  Scientific 
  Papers, 
  vol. 
  v. 
  p. 
  538. 
  

  

  t 
  Proc. 
  Roy. 
  Soc. 
  vol. 
  xlvii. 
  p. 
  364 
  (1890) 
  j 
  Scientific 
  Papers, 
  vol. 
  iii. 
  

   p. 
  349. 
  

  

  \ 
  Phil. 
  Mag. 
  vol. 
  xlviii. 
  p. 
  321 
  (1899); 
  Scientific 
  Papers, 
  vol. 
  iv. 
  

   p. 
  430. 
  

  

  