﻿276 
  A. 
  M. 
  Mayer— 
  On 
  the 
  Flotation 
  of 
  

  

  on 
  another 
  day 
  5 
  hours. 
  The 
  same 
  ring 
  loaded 
  so 
  that 
  it 
  

   lacked 
  30 
  per 
  cent 
  of 
  the 
  breaking 
  weight 
  floated 
  during 
  66 
  

   hours. 
  The 
  contamination 
  of 
  the 
  water 
  seemed 
  more 
  rapid 
  

   during 
  dry, 
  windy 
  and 
  dusty 
  weather 
  than 
  during, 
  or 
  just 
  after 
  

   a 
  rain. 
  The 
  contamination, 
  however, 
  also 
  proceeds 
  from 
  the 
  

   vessel, 
  either 
  of 
  glass 
  or 
  of 
  metal, 
  holding 
  the 
  water, 
  as 
  shown 
  

   by 
  Miss 
  Agnes 
  Pockels 
  of 
  Brunswick, 
  Germany.* 
  I 
  have 
  not 
  

   given 
  any 
  study 
  to 
  the 
  causes 
  of 
  the 
  contamination 
  of 
  a 
  surface 
  

   of 
  water 
  exposed 
  in 
  the 
  open 
  air, 
  because 
  the 
  results 
  with 
  the 
  

   ring, 
  though 
  curious, 
  are 
  of 
  little 
  value 
  unless 
  connected 
  with 
  

   other 
  observations 
  on 
  the 
  conditions 
  of 
  the 
  atmosphere. 
  It 
  

   may 
  be 
  that 
  a 
  floating 
  platinum 
  ring 
  may 
  be 
  of 
  use 
  in 
  deter- 
  

   mining 
  the 
  relative 
  amounts 
  of 
  dirt 
  or 
  dust 
  in 
  the 
  air 
  on 
  differ- 
  

   ent 
  days; 
  but 
  to 
  be 
  used 
  for 
  this 
  purpose 
  one 
  must 
  first 
  

   accurately 
  find 
  out 
  how 
  much 
  of 
  the 
  contamination 
  is 
  due 
  to 
  

   the 
  substance 
  of 
  the 
  vessel 
  by 
  experiments 
  make 
  on 
  water 
  in 
  

   the 
  trough 
  of 
  Miss 
  Pockels 
  inclosed 
  in 
  an 
  air-tight 
  vessel. 
  

  

  Several 
  pleasing 
  experiments 
  may 
  be 
  made 
  with 
  the 
  platinum 
  

   ring 
  floated 
  on 
  water 
  in 
  the 
  trough 
  devised 
  by 
  Miss 
  Pockels. 
  

   This 
  ingenious 
  and 
  simple 
  invention^ 
  consists 
  of 
  a 
  trough 
  of 
  

   tinned 
  iron 
  70 
  cm 
  long, 
  5 
  cra 
  wide,' 
  and 
  2 
  C!n 
  deep, 
  filled 
  

   to 
  its 
  brim 
  with 
  water. 
  A 
  strip 
  of 
  metal 
  longer 
  than 
  the 
  

   width 
  of 
  the 
  trough 
  is 
  placed 
  athwart 
  the 
  latter 
  with 
  the 
  plane 
  

   of 
  the 
  strip 
  in 
  a 
  vertical 
  position. 
  The 
  lower 
  edge 
  of 
  the 
  strip 
  

   touches 
  the 
  surface 
  of 
  the 
  water. 
  By 
  sliding 
  the 
  strip 
  from 
  

   the 
  extreme 
  end 
  of 
  the 
  trough 
  the 
  contaminated 
  surface 
  of 
  the 
  

   water 
  is 
  made 
  smaller 
  and 
  more 
  contaminated 
  on 
  the 
  side 
  of 
  

   the 
  strip 
  towards 
  which 
  this 
  is 
  moving, 
  while 
  the 
  surface 
  of 
  

   the 
  water 
  on 
  the 
  other 
  side 
  of 
  the 
  strip 
  has 
  been 
  swept 
  clean 
  

   and 
  may 
  be 
  regarded 
  as 
  a 
  clean 
  surface. 
  The 
  platinum 
  ring 
  is 
  

   floated 
  on 
  this 
  clean 
  surface 
  and 
  the 
  weight 
  required 
  to 
  sink 
  

   the 
  ring 
  is 
  determined. 
  Now 
  load 
  the 
  ring 
  till 
  its 
  weight 
  is 
  less 
  

   than 
  the 
  weight 
  required 
  to 
  sink 
  it 
  by 
  10, 
  20, 
  30, 
  etc., 
  percent. 
  

   If 
  the 
  ring 
  is 
  now 
  floated 
  near 
  one 
  end 
  of 
  the 
  trough 
  while 
  the 
  

   strip 
  of 
  metal 
  is 
  slid 
  along 
  from 
  the 
  other 
  end 
  of 
  the 
  trough 
  

   towards 
  the 
  ring, 
  the 
  surface 
  of 
  the 
  water 
  on 
  the 
  side 
  of 
  the 
  

   strip 
  toward 
  the 
  ring 
  becomes 
  more 
  and 
  more 
  contaminated 
  

   till 
  its 
  surface 
  tension 
  can 
  no 
  longer 
  hold 
  up 
  the 
  ring, 
  and 
  this 
  

   sinks. 
  Knowing 
  the 
  percentage 
  of 
  the 
  breaking 
  weight 
  with 
  

   which 
  the 
  ring 
  is 
  loaded 
  and 
  the 
  fraction 
  of 
  the 
  length 
  of 
  the 
  

   trough 
  to 
  which 
  the 
  strip 
  has 
  been 
  moved 
  when 
  the 
  ring 
  sank, 
  

   we 
  have 
  the 
  degree 
  of 
  contamination 
  of 
  the 
  water 
  of 
  the 
  

   trough 
  before 
  it 
  was 
  altered 
  by 
  the 
  sliding 
  strip. 
  

  

  There 
  is 
  no 
  difficulty 
  in 
  obtaining 
  a 
  contamination 
  surface. 
  

   The 
  surface 
  of 
  distilled 
  water 
  is 
  contaminated 
  soon 
  after 
  it 
  has 
  

  

  ^Surface 
  Tension. 
  A 
  letter 
  to 
  Lord 
  Rayleigh 
  from 
  Miss 
  Pockels. 
  Nature, 
  

   March 
  12, 
  1891. 
  

  

  