﻿928 
  

  

  Mr. 
  A. 
  Ferguson 
  on 
  tlie 
  Forces 
  acting 
  on 
  a 
  

  

  legitimate 
  or 
  not 
  depends 
  of 
  course 
  on 
  the 
  relative 
  values 
  of 
  

   r 
  x 
  and 
  a. 
  In 
  discussing 
  some 
  experiments 
  made 
  by 
  Gay- 
  

   Lussac 
  with 
  a 
  disk 
  5' 
  92 
  cm. 
  in 
  radius, 
  Laplace 
  obtains 
  from 
  

   his 
  formula 
  P 
  = 
  59*59 
  grams 
  weight, 
  assuming 
  for 
  a 
  2 
  the 
  

   value 
  "0756 
  sq.cm. 
  Gray-Lussac's 
  experiment 
  gives 
  P 
  = 
  59*40 
  

   grams 
  weight 
  — 
  " 
  ce 
  qui 
  s'accorde 
  aussi 
  bien 
  qu'on 
  peut 
  le 
  

   desirer, 
  avec 
  le 
  resultat 
  de 
  l'analyse 
  " 
  *. 
  

  

  But 
  if 
  we 
  take 
  into 
  account 
  the 
  third 
  term 
  of 
  equation 
  (xi.), 
  

   the 
  calculated 
  value 
  of 
  P 
  becomes 
  59*52 
  grams 
  weight, 
  in 
  

   still 
  closer 
  agreement 
  with 
  the 
  experimental 
  result. 
  The 
  

   effect 
  of 
  this 
  term 
  is, 
  therefore, 
  with 
  such 
  a 
  disk, 
  small 
  but 
  

   appreciable; 
  with 
  a 
  disk 
  above 
  7 
  or 
  8 
  cm. 
  in 
  radius 
  the 
  effect 
  

   of 
  this 
  third 
  term 
  is 
  negligible. 
  

  

  But 
  the 
  doubtfulness 
  of 
  the 
  assumption 
  italicised 
  above 
  t 
  

   considerably 
  minimises 
  the 
  practical 
  value 
  of 
  the 
  method. 
  

   Even 
  if 
  the 
  contact-angle 
  of 
  the 
  liquid 
  be 
  known, 
  it 
  is 
  by 
  no 
  

   means 
  certain 
  that 
  this 
  is 
  the 
  angle 
  at 
  which 
  the 
  liquid 
  meets 
  

   the 
  disk 
  along 
  an 
  edge. 
  

  

  This 
  objection 
  is 
  nullified 
  if 
  we 
  substitute 
  for 
  the 
  disk 
  a 
  

   segment 
  of 
  a 
  sphere 
  partly 
  immersed 
  in 
  the 
  liquid, 
  so 
  that 
  

   the 
  liquid 
  touches 
  the 
  sphere 
  round 
  a 
  small 
  circle. 
  In 
  spite 
  

   of 
  its 
  obvious 
  advantages 
  over 
  the 
  disk, 
  this 
  problem 
  does 
  not 
  

   seem 
  to 
  have 
  received 
  any 
  attention 
  from 
  either 
  analysts 
  or 
  

   experimenters. 
  

  

  Eur. 
  2. 
  

  

  Various 
  particular 
  cases 
  will 
  be 
  discussed 
  later; 
  for 
  the 
  

   present 
  we 
  confine 
  ourselves 
  to 
  the 
  case 
  (fig. 
  2) 
  in 
  which 
  the 
  

   vertex 
  of 
  the 
  sphere 
  is 
  just 
  on 
  a 
  level 
  with 
  the 
  general 
  

   surface 
  of 
  the 
  liquid. 
  

  

  We 
  further 
  assume 
  that 
  the 
  radius 
  (R) 
  of 
  the 
  sphere 
  is 
  

  

  * 
  Laplace, 
  op. 
  cit. 
  p. 
  54. 
  (It 
  is 
  to 
  be 
  noted 
  that 
  throughout, 
  in 
  

   comparing 
  theory 
  •with 
  experiment, 
  Laplace 
  ignores 
  the 
  effect 
  of 
  

   temperature 
  variations, 
  excepting 
  in 
  so 
  far 
  as 
  they 
  affect 
  the 
  density 
  of 
  

   the 
  liquid.) 
  

  

  t 
  On 
  this 
  point 
  cf. 
  Mathieu, 
  < 
  Theorie 
  de 
  la 
  Capillarity' 
  p. 
  127. 
  

  

  