﻿Disks 
  and 
  Rings 
  of 
  Metal. 
  

  

  Fig. 
  2. 
  

  

  261 
  

  

  .A 
  

  

  c 
  

  

  R 
  

  

  =U= 
  P 
  

   T 
  

  

  was 
  fastened 
  to 
  the 
  slide 
  and 
  micrometer 
  screw 
  used 
  in 
  deter- 
  

   mining 
  A, 
  and 
  the 
  plate 
  of 
  aluminum 
  was 
  brought 
  down 
  to 
  the 
  

   surface 
  of 
  the 
  water 
  contained 
  in 
  a 
  tank, 
  T, 
  having 
  sides 
  of 
  

   flat 
  glass. 
  The 
  Dumber 
  of 
  turns 
  of 
  the 
  micrometer 
  screw 
  to 
  

   bring 
  the 
  plate 
  P 
  to 
  the 
  depth 
  of 
  rupture 
  of 
  the 
  water 
  was 
  

   ascertained. 
  Then 
  it 
  was 
  easy 
  to 
  depress 
  the 
  square 
  plate 
  in 
  

   the 
  water 
  till 
  it 
  was 
  just 
  on 
  the 
  point 
  of 
  rupture. 
  While 
  in 
  

   this 
  position 
  the 
  edge 
  of 
  the 
  plate 
  was 
  viewed 
  in 
  the 
  micro- 
  

   scope, 
  M, 
  provided 
  with 
  a 
  camera 
  lucida, 
  C, 
  and 
  a 
  drawing 
  was 
  

   made 
  of 
  the 
  contour 
  of 
  the 
  depressed 
  water-surface. 
  It 
  is 
  true 
  

   that 
  there 
  must 
  be 
  some 
  distortion 
  of 
  this 
  contour, 
  caused 
  by 
  

   refraction 
  of 
  the 
  depressed 
  water, 
  but 
  it 
  is 
  the 
  only 
  way 
  by 
  

   which 
  I 
  have 
  been 
  able 
  to 
  obtain 
  even 
  an 
  approximation 
  to 
  the 
  

   contour. 
  The 
  microscope 
  objective, 
  called 
  a 
  3-inch, 
  was 
  of 
  

   large 
  aperture 
  and 
  of 
  the 
  low 
  magnifying 
  power 
  of 
  11J 
  

   diameters. 
  

  

  Fig. 
  3. 
  

  

  Fig. 
  3 
  is 
  the 
  average 
  of 
  several 
  drawings 
  of 
  the 
  contour. 
  

   The 
  engraving 
  shows 
  the 
  disk, 
  the 
  depressed 
  water 
  and 
  the 
  

   contour 
  of 
  the 
  latter, 
  magnified 
  7-J- 
  diameters. 
  If 
  the 
  depressed 
  

   surface 
  met 
  the 
  edge 
  of 
  the 
  disk 
  normally, 
  then 
  the 
  center 
  of 
  

   the 
  radius 
  of 
  curvature 
  of 
  the 
  lowest 
  portion 
  s, 
  of 
  the 
  surface 
  

  

  