﻿93-1 
  Forces 
  on 
  Solid 
  Sphere 
  in 
  contact 
  with 
  Liquid 
  Surface. 
  

   The 
  mean 
  of 
  the 
  twenty 
  experiments 
  gives 
  

   T 
  I5 
  = 
  73*40 
  dynes 
  per 
  cm., 
  

  

  with 
  a 
  probable 
  error 
  of 
  +'03. 
  But 
  the 
  series 
  G 
  is 
  notably 
  

   lower 
  than 
  the 
  rest, 
  and 
  judging 
  both 
  from 
  the 
  consistency 
  

   of 
  the 
  three 
  readings 
  G 
  amongst 
  themselves, 
  and 
  the 
  con- 
  

   sistency 
  of 
  the 
  remaining 
  17 
  readings, 
  which 
  have 
  been 
  

   taken 
  on 
  9 
  different 
  specimens 
  of 
  water, 
  it 
  seems 
  almost 
  

   certain 
  that 
  the 
  lowness 
  of 
  the 
  readings 
  G 
  is 
  due 
  to 
  the 
  

   presence 
  of 
  traces 
  of 
  surface 
  impurities. 
  Rejecting 
  the 
  

   series 
  G 
  in 
  taking 
  the 
  mean, 
  we 
  have 
  

  

  T 
  15 
  = 
  73-45 
  + 
  -023 
  ^^. 
  

  

  cm. 
  

  

  For 
  convenience 
  of 
  comparison, 
  a 
  table 
  of 
  values 
  due 
  to 
  

   other 
  experimenters 
  is 
  appended. 
  

  

  T 
  l5 
  - 
  

  

  Observer. 
  

  

  Method. 
  

  

  73-26 
  

   73-46 
  

   7345 
  

   73-76 
  

   73-72 
  

   74-30 
  

   72-78 
  

   7i-22 
  

  

  Volkmann 
  . 
  .. 
  

   Donike 
  ... 
  ..... 
  

  

  Hall 
  

  

  Sentis 
  

  

  Capillary 
  tubes. 
  

  

  Capillary 
  tubes. 
  

  

  Weighing 
  tension 
  in 
  film 
  

  

  Capillary 
  tubes. 
  

  

  Ripples. 
  

  

  Weaves 
  on 
  jet. 
  

  

  Waves 
  on 
  jet. 
  

  

  Eippled 
  surface 
  used 
  as 
  

   iraction 
  grating. 
  

  

  clif- 
  

  

  Dorsey 
  

  

  Pedersen 
  

  

  Bohr 
  

  

  Kalahne 
  

  

  

  The 
  method, 
  considered 
  as 
  a 
  practical 
  means 
  for 
  the 
  

   determination 
  of 
  surface 
  tensions, 
  shares, 
  with 
  several 
  others 
  

   of 
  the 
  well-known 
  methods, 
  the 
  disadvantage 
  of 
  requiring 
  a 
  

   knowledge 
  of 
  contact-angles. 
  Apart 
  from 
  this 
  qualification, 
  

   however, 
  it 
  is 
  extremely 
  consistent 
  in 
  practice, 
  and 
  very 
  

   sensitive. 
  As 
  the 
  above 
  table 
  shows, 
  a 
  change 
  of 
  surface 
  

   tension 
  due 
  to 
  a 
  rise 
  of 
  *2 
  or 
  *3 
  degree 
  in 
  temperature 
  can 
  

   be 
  readily 
  and 
  accurately 
  estimated. 
  In 
  this 
  respect 
  the 
  

   sensitiveness 
  of 
  the 
  method 
  is 
  comparable 
  with 
  that 
  of 
  the 
  

   " 
  capillary 
  multiplier," 
  and 
  considerably 
  exceeds 
  that 
  of 
  

   the 
  classic 
  capillary 
  tube. 
  

  

  University 
  College 
  of 
  North 
  Wales, 
  

   Bangor. 
  

  

  July 
  1913. 
  

  

  