﻿• 
  Disks 
  and 
  Rings 
  of 
  Metal. 
  277 
  

  

  been 
  poured 
  into 
  the 
  trough 
  ; 
  and 
  no 
  doubt 
  was 
  contaminated 
  

   before 
  it 
  was 
  poured 
  from 
  the 
  bottle. 
  If, 
  however, 
  a 
  greater 
  

   degree 
  of 
  contamination 
  of 
  surface 
  is 
  required 
  it 
  may 
  be 
  

   obtained 
  by 
  introducing 
  into 
  the 
  water 
  the 
  point 
  of 
  a 
  needle 
  

   which 
  has 
  been 
  coated 
  with 
  a 
  thin 
  film 
  of 
  oil, 
  or, 
  by 
  scraping 
  

   camphor 
  over 
  the 
  surface 
  of 
  the 
  water. 
  A 
  very 
  thin 
  film 
  of 
  

   oil, 
  whose 
  thickness 
  Lord 
  Rayleigh 
  has 
  fixed 
  as 
  equal 
  to 
  \\ 
  

   millionth 
  of 
  a 
  millimeter, 
  or 
  % 
  \-$ 
  of 
  the 
  length 
  of 
  a 
  wave 
  of 
  

   yellow 
  light, 
  is 
  sufficient 
  to 
  stop 
  the 
  motions 
  of 
  minute, 
  thin 
  

   scrapings 
  of 
  camphor.* 
  If 
  the 
  motions 
  of 
  the 
  camphor, 
  how- 
  

   ever, 
  continue 
  with 
  the 
  degree 
  of 
  contamination 
  we 
  have 
  given 
  

   the 
  water, 
  we 
  can 
  stop 
  these 
  motions 
  by 
  increasing 
  the 
  con- 
  

   tamination 
  on 
  sliding 
  the 
  metal 
  strip 
  along 
  the 
  trough 
  and 
  con- 
  

   tracting 
  the 
  contaminated 
  surface. 
  If 
  the 
  ring 
  floating 
  on 
  this 
  

   portion 
  of 
  the 
  liquid 
  is 
  now 
  loaded 
  till 
  it 
  sinks, 
  we 
  have 
  the 
  

   means 
  of 
  knowing 
  the 
  diminution 
  of 
  the 
  surface 
  tension 
  

   required 
  to 
  stop 
  the 
  motions 
  of 
  the 
  camphor, 
  f 
  

  

  If 
  the 
  ring 
  is 
  placed 
  near 
  one 
  end 
  of 
  the 
  trough 
  and 
  the 
  

   strip 
  of 
  metal 
  is 
  slid 
  from 
  the 
  extreme 
  end 
  of 
  the 
  trough 
  

   towards 
  the 
  ring, 
  but 
  not 
  near 
  enough 
  to 
  it 
  to 
  cause 
  such 
  

   lowering 
  of 
  surface 
  tension 
  that 
  the 
  ring 
  sinks, 
  one 
  will 
  observe 
  

   the 
  ring 
  to 
  move 
  slightly 
  away 
  from 
  the 
  moving 
  strip. 
  This 
  

   is 
  owing 
  to 
  the 
  contamination 
  of 
  the 
  surface 
  being 
  slightly 
  

   greater, 
  and 
  the 
  surface 
  tension 
  lower, 
  near 
  the 
  side 
  of 
  the 
  

   strip 
  towards 
  the 
  ring 
  than 
  it 
  is 
  at 
  a 
  distance 
  from 
  the 
  strip, 
  

   near 
  to 
  and 
  beyond 
  the 
  floating 
  ring. 
  The 
  consequence 
  is 
  that 
  

   the 
  surface 
  film 
  surrounding 
  the 
  ring 
  and 
  beyond 
  it 
  contracts 
  

   and 
  carries 
  the 
  ring 
  away 
  from 
  the 
  strip. 
  The 
  strip 
  now 
  

   remaining 
  stationary, 
  we 
  have 
  a 
  lower 
  tension 
  on 
  the 
  contami- 
  

   nated 
  or 
  ring 
  side 
  of 
  the 
  strip 
  than 
  on 
  the 
  other 
  side, 
  where 
  the 
  

   surface 
  of 
  the 
  water 
  is 
  clean; 
  therefore 
  on 
  sliding 
  the 
  strip 
  

   backwards 
  with 
  a 
  gradually 
  increasing 
  velocity 
  over 
  this 
  clean 
  

   surface, 
  or, 
  on 
  removing 
  the 
  strip 
  from 
  the 
  trough, 
  the 
  clean 
  

   surface 
  contracts 
  and 
  keeps 
  on 
  contracting 
  till 
  it 
  has 
  so 
  stretched 
  

   the 
  contaminated 
  surface 
  that 
  it 
  covers 
  uniformly 
  the 
  whole 
  

   surface 
  of 
  the 
  trough. 
  The 
  ring, 
  hung 
  in 
  this 
  surface 
  which 
  is 
  

   being 
  stretched, 
  moves 
  with 
  it 
  and 
  is 
  seen 
  to 
  go 
  rapidly 
  towards 
  

   the 
  other 
  end 
  of 
  the 
  trough. 
  

  

  Metals 
  and 
  glass 
  float 
  on 
  water 
  when 
  the 
  film 
  of 
  air 
  condensed 
  on 
  

   their 
  surfaces 
  has 
  been 
  driven 
  off 
  by 
  heat. 
  

  

  If 
  platinum, 
  gold, 
  or 
  silver 
  wire 
  of 
  T 
  4 
  Q- 
  mm 
  in 
  diameter 
  is 
  

   formed 
  into 
  a 
  ring, 
  heated 
  to 
  redness 
  and 
  when 
  cold 
  placed 
  on 
  

  

  * 
  On 
  Foam. 
  A 
  lecture 
  by 
  Lord 
  Rayleigh 
  before 
  the 
  Royal 
  Institution. 
  March 
  

   28, 
  1890. 
  

  

  f 
  I 
  have 
  been 
  prevented 
  from 
  making 
  this 
  interesting 
  experiment 
  by 
  a 
  painful 
  

   and 
  long 
  illness 
  from 
  which 
  I 
  have 
  not 
  yet 
  recovered. 
  

  

  