﻿158 
  Lord 
  Rayleigh 
  on 
  the 
  Lubricating 
  

  

  thick 
  plate 
  glass 
  and 
  a 
  small 
  glass 
  bottle 
  weighing 
  about 
  

   4 
  oz. 
  The 
  diameter 
  of 
  the 
  bottle 
  is 
  4^ 
  cm., 
  and 
  the 
  bottom 
  

   is 
  concave, 
  bounded 
  by 
  a 
  rim 
  which 
  is 
  not 
  ground 
  but 
  makes 
  

   a 
  fairly 
  good 
  fit 
  with 
  the 
  plate. 
  The 
  slab 
  is 
  placed 
  upon 
  a 
  

   slope, 
  and 
  the 
  subject 
  of 
  observation 
  is 
  the 
  slipping 
  of 
  the 
  

   bottle 
  upon 
  it. 
  If 
  we 
  begin 
  with 
  surfaces 
  washed 
  and 
  well 
  

   rubbed 
  with 
  an 
  ordinary 
  clotb, 
  or 
  gone 
  over 
  with 
  a 
  recently 
  

   wiped 
  hand, 
  we 
  find 
  that 
  at 
  a 
  suitable 
  inclination 
  the 
  con- 
  

   ditions 
  are 
  uniform, 
  the 
  bottle 
  starting 
  slowly 
  and 
  moving 
  

   freely 
  from 
  every 
  position. 
  If 
  now 
  we 
  breathe 
  upon 
  the 
  

   slab, 
  maintained 
  in 
  a 
  fixed 
  position, 
  or 
  upon 
  the 
  bottle, 
  or 
  

   upon 
  both, 
  we 
  find 
  that 
  the 
  bottle 
  sticks 
  and 
  requires 
  very 
  

   sensible 
  forces 
  to 
  make 
  it 
  move 
  down. 
  A 
  like 
  result 
  ensues 
  

   when 
  the 
  contacts 
  are 
  thoroughly 
  wetted 
  with 
  water 
  instead 
  

   of 
  being 
  merely 
  damped. 
  When, 
  after 
  damping 
  with 
  the 
  

   breath, 
  evaporation 
  removes 
  the 
  moisture, 
  almost 
  complete 
  

   recovery 
  of 
  the 
  original 
  slipperiness 
  recurs. 
  

  

  In 
  the 
  slippery 
  condition 
  the 
  surfaces, 
  though 
  apparently 
  

   clean, 
  are 
  undoubtedly 
  coated 
  with 
  an 
  invisible 
  greasy 
  

   layer. 
  If, 
  after 
  a 
  thorough 
  washing 
  and 
  rubbing 
  under 
  the 
  

   tap, 
  the 
  surfaces 
  are 
  dried 
  by 
  evaporation 
  after 
  shaking 
  off 
  

   as 
  much 
  of 
  the 
  water 
  as 
  possible, 
  they 
  are 
  found 
  to 
  be 
  sticky 
  

   as 
  compared 
  with 
  the 
  condition 
  after 
  wiping. 
  A 
  better 
  

   experiment 
  was 
  made 
  with 
  substitution 
  of 
  a 
  strip 
  of 
  thinner 
  

   glass 
  about 
  5 
  cm. 
  wide 
  for 
  the 
  thick 
  slab. 
  This 
  was 
  heated 
  

   strongly 
  by 
  an 
  alcohol 
  flame, 
  preferably 
  with 
  use 
  of 
  a 
  blow- 
  

   pipe. 
  At 
  a 
  certain 
  angle 
  of 
  inclination 
  the 
  bottle 
  was 
  held 
  

   everywhere, 
  but 
  on 
  going 
  over 
  the 
  surface 
  with 
  the 
  fingers, 
  

   not 
  purposely 
  greased, 
  tree 
  movement 
  ensued. 
  As 
  might 
  

   have 
  been 
  expected, 
  the 
  clean 
  surface 
  is 
  sticky 
  as 
  compared 
  

   with 
  one 
  slightly 
  greased 
  ; 
  the 
  difficulty 
  so 
  far 
  is 
  to 
  explain 
  

   the 
  effect 
  of 
  moisture 
  upon 
  a 
  surface 
  already 
  slightly 
  greased. 
  

   It 
  was 
  not 
  surprising 
  that 
  the 
  effect 
  of 
  alcohol 
  was 
  similar 
  

   to 
  that 
  of 
  water. 
  

  

  At 
  this 
  stage 
  it 
  was 
  important 
  to 
  make 
  sure 
  that 
  the 
  

   stickiness 
  due 
  to 
  water 
  was 
  not 
  connected 
  with 
  the 
  minute- 
  

   ness 
  of 
  the 
  quantity 
  in 
  operation. 
  Accordingly 
  a 
  glass 
  plate 
  

   was 
  mounted 
  at 
  a 
  suitable 
  angle 
  in 
  a 
  dish 
  filled 
  with 
  water. 
  

   Upon 
  this 
  fully 
  drowned 
  surface 
  the 
  bottle 
  stuck, 
  the 
  inclina- 
  

   tion 
  being 
  such 
  that 
  on 
  the 
  slightest 
  greasing 
  the 
  motion 
  

   became 
  free. 
  In 
  another 
  experiment 
  the 
  water 
  in 
  the 
  dish 
  

   was 
  replaced 
  by 
  paraffin 
  oil. 
  There 
  was 
  decided 
  stickiness 
  

   as 
  compared 
  with 
  surfaces 
  slightly 
  greasy. 
  

  

  The 
  better 
  to 
  guard 
  against 
  the 
  ordinary 
  operation 
  of 
  sur- 
  

   face 
  tension, 
  the 
  weight 
  of 
  the 
  bottle 
  was 
  increased 
  by 
  

   inclusion 
  of 
  mercury 
  until 
  it 
  reached 
  20 
  oz., 
  but 
  without 
  

  

  