﻿Disks 
  and 
  Rings 
  of 
  Metal. 
  278 
  

  

  From 
  experiments 
  on 
  Iron 
  ring 
  _ 
  . 
  . 
  '0802 
  

  

  " 
  " 
  tinned 
  Iron 
  ring.. 
  _ 
  "0810 
  

  

  " 
  " 
  Copper 
  " 
  ... 
  -0813 
  

  

  " 
  " 
  Brass 
  " 
  ... 
  '0810 
  

  

  " 
  " 
  German 
  Silver 
  " 
  ... 
  '0811 
  

  

  •0809 
  = 
  mean 
  

  

  The 
  maximum 
  value 
  exceeds 
  the 
  minimum 
  by 
  1'37 
  per 
  cent. 
  

   The 
  mean 
  difference 
  of 
  the 
  minimum 
  and 
  maximum 
  from 
  the 
  

   mean 
  is 
  y-Jy 
  of 
  the 
  mean. 
  

  

  From 
  these 
  experiments 
  on 
  the 
  rings, 
  and 
  from 
  the 
  value 
  

   of 
  A 
  deduced 
  from 
  them, 
  it 
  appears 
  that 
  W 
  = 
  2T 
  + 
  P 
  repre- 
  

   sents 
  the 
  equation 
  of 
  the 
  forces 
  acting 
  on 
  a 
  floating 
  ring. 
  

  

  On 
  the 
  value 
  of 
  the 
  constant 
  of 
  the 
  surface-tension 
  of 
  water. 
  

  

  The 
  mean 
  of 
  twenty-eight 
  determinations 
  of 
  the 
  surface 
  

   tension 
  of 
  water 
  in 
  grams 
  per 
  centimeter, 
  made 
  by 
  physicists 
  

   during 
  the 
  past 
  sixty 
  years, 
  is 
  '0772. 
  Nineteen 
  of 
  these 
  deter- 
  

   minations 
  were 
  deduced 
  from 
  measures 
  on 
  the 
  ascent 
  of 
  water 
  

   in 
  capillary 
  tubes 
  and 
  give 
  a 
  mean 
  value 
  of 
  *0769. 
  These 
  vary 
  

   from 
  -0747 
  by 
  Quincke 
  to 
  '0812 
  as 
  determined 
  by 
  Simon. 
  

   The 
  latter 
  is 
  8*7 
  per 
  cent 
  greater 
  than 
  the 
  former. 
  The 
  

   remaining 
  nine 
  determinations 
  of 
  the 
  twenty- 
  eight 
  were 
  made 
  

   by 
  measurements 
  on 
  drops 
  and 
  bubbles, 
  adhesion 
  of 
  disks, 
  pen- 
  

   dent 
  drops, 
  weight 
  of 
  elevated 
  meniscus 
  adhering 
  to 
  a 
  rectan- 
  

   gular 
  plate, 
  extent 
  and 
  time 
  of 
  oscillations 
  of 
  falling 
  drops, 
  

   wave 
  length 
  of 
  ripples, 
  and 
  by 
  direct 
  measure 
  of 
  tension 
  of 
  a 
  

   film 
  of 
  water 
  acting 
  on 
  a 
  suspended 
  rectangular 
  frame. 
  These 
  

   vary 
  from 
  Lenard's 
  (0740, 
  obtained 
  from 
  observations 
  on 
  the 
  

   extent 
  and 
  time 
  of 
  oscillations 
  of 
  falling 
  drops, 
  to 
  Quincke's 
  

   '0827, 
  deduced 
  from 
  measurements 
  on 
  bubbles 
  and 
  drops. 
  

   Quincke's 
  value 
  is 
  11*7 
  per 
  cent 
  higher 
  than 
  Lenard's. 
  

  

  The 
  surface 
  tensions 
  given 
  are 
  reduced 
  to 
  their 
  value 
  at 
  0° 
  

   by 
  Brunner's 
  formula, 
  and 
  are 
  taken 
  from 
  a 
  paper 
  by 
  T. 
  

   Proctor 
  Hall, 
  New 
  methods 
  of 
  measuring 
  the 
  surface 
  tension 
  

   of 
  liquids, 
  Phil. 
  Mag., 
  Nov. 
  1893, 
  in 
  which 
  paper 
  a 
  complete 
  

   list 
  of 
  the 
  determinations 
  of 
  the 
  surface 
  tension 
  of 
  water 
  is 
  

   given 
  in 
  dynes. 
  I 
  have 
  reduced 
  them 
  to 
  grams 
  per 
  centimeter 
  

   by 
  dividing 
  by 
  980*9. 
  

  

  The 
  value 
  *0809 
  given 
  by 
  my 
  experiments 
  on 
  the 
  floating 
  

   rings 
  is 
  3J- 
  per 
  cent 
  higher 
  than 
  '0772, 
  the 
  mean 
  of 
  all 
  the 
  deter- 
  

   minations 
  on 
  the 
  surface 
  tension 
  of 
  water. 
  However, 
  Quincke* 
  

   gives 
  -0827 
  ; 
  Timberg,f 
  '0820 
  ; 
  Weinberg,:): 
  '0816, 
  and 
  Simon,§ 
  

   •0812. 
  

  

  *Pogg. 
  Ann., 
  cxxxix, 
  p. 
  253. 
  f 
  Wied. 
  Ann., 
  xxx, 
  p. 
  545, 
  1887. 
  

  

  % 
  Beibl., 
  xvi, 
  p. 
  496, 
  1892. 
  § 
  Ann. 
  Chim. 
  Phys., 
  xxxii, 
  p. 
  5, 
  1851. 
  

  

  