﻿Disks 
  and 
  JRings 
  of 
  Metal. 
  269 
  

  

  along 
  the 
  lowest 
  part 
  of 
  either 
  of 
  the 
  depressed 
  surfaces 
  of 
  

   water 
  when 
  these 
  surfaces 
  are 
  nearly 
  m 
  contact, 
  or 
  in 
  actual 
  

   contact, 
  and 
  therefore 
  when 
  the 
  circumferences 
  of 
  these 
  sur- 
  

   faces 
  may 
  be 
  regarded 
  as 
  equal 
  to 
  the 
  circumference 
  of 
  the 
  

   axis 
  of 
  the 
  ring. 
  Then, 
  

  

  W=2T 
  + 
  P. 
  

  

  If 
  we 
  divide 
  W 
  by 
  the 
  circumference 
  of 
  the 
  axis 
  of 
  the 
  

   ring 
  in 
  centimeters 
  we 
  obtain, 
  as 
  the 
  average 
  of 
  30 
  experi- 
  

   ments, 
  -1696 
  gram 
  per 
  centimeter. 
  The 
  upward 
  hydrostatic 
  

   pressure 
  will 
  be 
  either 
  -01186 
  or 
  -00784 
  according 
  as 
  the 
  two 
  

   opposed 
  films 
  of 
  water 
  are 
  as 
  shown 
  in 
  fig. 
  9 
  or 
  as 
  in 
  fig. 
  10. 
  

  

  If 
  as 
  in 
  fig. 
  9, 
  then 
  A 
  = 
  ' 
  1696 
  "' 
  Q1186 
  _ 
  i 
  _ 
  C0S 
  2£ 
  = 
  -07895. 
  If 
  

  

  as 
  in 
  fig. 
  10, 
  then 
  A 
  = 
  ' 
  1696 
  ~' 
  QQ78 
  4 
  ^cos 
  2i° 
  = 
  '08095. 
  

  

  A 
  ring 
  is 
  formed 
  by 
  bending 
  wire, 
  l 
  mm 
  thick, 
  around 
  a 
  

   cylinder 
  or 
  a 
  cone, 
  so 
  that 
  the 
  axis 
  of 
  the 
  ring 
  shall 
  be 
  in 
  a 
  

   plane 
  ; 
  in 
  other 
  words, 
  so 
  that 
  the 
  ring 
  shall 
  be 
  flat. 
  To 
  ob- 
  

   tain 
  a 
  flat 
  ring 
  is 
  not 
  easy, 
  often 
  only 
  after 
  several 
  trials 
  is 
  it 
  

   secured. 
  Its 
  ends 
  are 
  then 
  neatly 
  soldered 
  together 
  and 
  the 
  

   solder 
  outside 
  the 
  juncture 
  is 
  carefully 
  removed. 
  Over 
  a 
  diam- 
  

   eter 
  of 
  the 
  ring 
  is 
  soldered 
  a 
  wire 
  of 
  T 
  2 
  5 
  mm 
  thick, 
  raised 
  above 
  

   the 
  plane 
  of 
  the 
  ring 
  as 
  shown 
  in 
  fig. 
  4. 
  On 
  the 
  top 
  of 
  this 
  

   wire, 
  and 
  cencentric 
  with 
  the 
  circumference 
  of 
  the 
  ring, 
  is 
  

   soldered 
  a 
  cup 
  made 
  of 
  thin 
  (| 
  mm 
  ) 
  brass. 
  The 
  ring 
  is 
  now 
  

   polished, 
  and 
  cleaned 
  by 
  the 
  successive 
  use 
  of 
  ether, 
  strong 
  

   alcohol 
  and 
  distilled 
  water. 
  After 
  it 
  has 
  remained 
  several 
  

   hours 
  under 
  cover 
  it 
  may 
  be 
  experimented 
  with. 
  

  

  The 
  weight 
  required 
  to 
  force 
  the 
  ring 
  through 
  the 
  surface 
  of 
  

   the 
  water 
  is 
  obtained 
  by 
  pouring 
  into 
  the 
  cup 
  of 
  the 
  floating 
  

   ring 
  a 
  fine 
  stream 
  of 
  sand 
  issuing 
  from 
  a 
  small 
  smooth 
  aperture 
  

   in 
  a 
  bent 
  glass 
  tube 
  which 
  goes 
  through 
  a 
  cork 
  in 
  a 
  bottle 
  con- 
  

   taining 
  the 
  sand. 
  This 
  sand 
  is 
  from 
  Minnesota. 
  It 
  is 
  wind- 
  

   blown, 
  the 
  grains 
  being 
  globular, 
  or 
  ovoid. 
  It 
  was 
  passed 
  

   through 
  a 
  sieve 
  having 
  100 
  meshes 
  to 
  the 
  inch. 
  It 
  is 
  hardly 
  

   possible 
  to 
  stop 
  the 
  running 
  of 
  the 
  sand 
  into 
  the 
  cup 
  at 
  the 
  

   moment 
  the 
  ring 
  sinks. 
  From 
  several 
  experiments 
  I 
  estimated 
  

   that 
  on 
  the 
  average 
  about 
  three 
  milligrams 
  of 
  sand 
  were 
  

   poured 
  into 
  the 
  cup 
  after 
  the 
  ring 
  had 
  really 
  broken 
  through 
  

   the 
  water, 
  and 
  this 
  quantity 
  was 
  subtracted 
  from 
  the 
  breaking- 
  

   weight 
  of 
  each 
  experiment. 
  Fresh 
  distilled 
  water 
  was 
  used 
  in 
  

   each 
  experiment. 
  On 
  the 
  average, 
  each 
  experiment 
  occupied 
  

   twenty-five 
  seconds. 
  

  

  The 
  depth 
  to 
  which 
  a 
  ring 
  has 
  descended 
  in 
  the 
  depressed 
  

   surface 
  of 
  the 
  water 
  at 
  the 
  moment 
  the 
  ring 
  sinks 
  was 
  deter- 
  

   mined 
  as 
  follows 
  : 
  A 
  ring 
  of 
  5'3 
  cm 
  in 
  diameter 
  made 
  of 
  tinned 
  

  

  A.M. 
  Jour. 
  Scl— 
  Fourth 
  Series, 
  Vol. 
  Ill, 
  No. 
  16. 
  — 
  April, 
  1897. 
  

   19 
  

  

  