﻿Disks 
  and 
  Rings 
  of 
  Metal. 
  279 
  

  

  is 
  attracted 
  by 
  the 
  wire 
  so 
  that 
  it 
  adheres 
  to 
  it 
  with 
  such 
  force 
  

   that 
  it 
  can 
  take 
  the 
  curvature 
  required 
  to 
  withstand 
  the 
  inward 
  

   hydrostatic 
  pressure 
  on 
  the 
  two 
  depressed 
  water 
  surfaces. 
  

   Another 
  observation 
  is 
  of 
  interest 
  here. 
  On 
  observing 
  the 
  wire 
  

   between 
  the 
  depressed 
  sheets 
  of 
  water 
  through 
  a 
  microscope, 
  as 
  

   in 
  tig. 
  6, 
  one 
  does 
  not 
  see 
  the 
  opposite 
  surfaces 
  of 
  the 
  water 
  

   gradually 
  and 
  smoothly 
  slide 
  over 
  the 
  wire 
  and 
  approach 
  

   one 
  another 
  as 
  the 
  wire 
  goes 
  deeper 
  and 
  deeper 
  in 
  the 
  depres- 
  

   sion, 
  but 
  the 
  terminal 
  edges 
  of 
  the 
  depressed 
  water 
  surfaces 
  

   leave 
  the 
  wire 
  to 
  approach 
  one 
  another 
  in 
  a 
  series 
  of 
  jumps. 
  

   These 
  releases 
  of 
  the 
  two 
  edges 
  of 
  the 
  water 
  surfaces 
  from 
  the 
  

   wire 
  do 
  not 
  take 
  place 
  uniformly 
  and 
  simultaneously 
  along 
  the 
  

   whole 
  of 
  these 
  edges, 
  but 
  take 
  place 
  at 
  many 
  points 
  irregularly 
  

   distributed 
  along 
  the 
  lines 
  of 
  demarkation 
  of 
  the 
  wire 
  and 
  water. 
  

  

  The 
  attraction 
  existing 
  between 
  the 
  wire 
  and 
  the 
  water 
  is 
  

   shown 
  by 
  lifting 
  a 
  floating 
  ring 
  above 
  the 
  general 
  surface 
  of 
  the 
  

   water 
  when 
  the 
  water 
  adheres 
  to 
  the 
  ring 
  and 
  may 
  be 
  lifted 
  

   several 
  millimeters. 
  If 
  the 
  ring 
  be 
  lifted 
  quickly 
  we 
  often 
  

   obtain 
  a 
  catenoid 
  of 
  elevated 
  water-film 
  apparently 
  a 
  centi- 
  

   meter 
  or 
  more 
  in 
  height. 
  When 
  the 
  elevated 
  film 
  breaks 
  it 
  

   generally 
  forms 
  into 
  drops 
  regularly 
  spaced 
  around 
  the 
  ring. 
  

  

  The 
  film 
  of 
  air 
  on 
  the 
  surfaces 
  of 
  the 
  rings 
  must 
  be 
  very 
  

   thin, 
  probably 
  a 
  small 
  fraction 
  of 
  the 
  radius 
  of 
  molecular 
  

   activity 
  which, 
  according 
  to 
  Plateau 
  and 
  Quincke, 
  is 
  about 
  

   O00005 
  mm 
  , 
  or 
  ¥ 
  V 
  of 
  a 
  micron, 
  or 
  about 
  ^ 
  2 
  of 
  the 
  wave 
  length 
  of 
  

   sodium 
  light. 
  If, 
  however, 
  the 
  air 
  be 
  condensed 
  on 
  the 
  metals 
  to 
  

   the 
  same 
  degree 
  that 
  oxygen 
  is 
  occluded 
  by 
  platinum 
  black, 
  the 
  

   air 
  film 
  may 
  have 
  the 
  density 
  of 
  water 
  and 
  its 
  attraction 
  may 
  

   be 
  of 
  an 
  order 
  approaching 
  that 
  of 
  the 
  metal 
  itself 
  for 
  water. 
  

   This 
  condition, 
  w{iich 
  probably 
  exists, 
  renders 
  futile 
  the 
  deter- 
  

   mination 
  of 
  the 
  thickness 
  of 
  the 
  air 
  film 
  by 
  optical 
  methods. 
  

   Professor 
  Wright, 
  of 
  Yale 
  University, 
  suggested 
  to 
  me 
  to 
  

   determine 
  if 
  total 
  reflection 
  took 
  place 
  from 
  a 
  water 
  surface 
  

   which 
  was 
  in 
  contact 
  with 
  a 
  surface 
  of 
  metal. 
  I 
  made 
  the 
  

   experiment 
  in 
  the 
  following 
  manner. 
  A 
  cubical 
  vessel 
  made 
  

   of 
  plates 
  of 
  glass, 
  such 
  as 
  is 
  used 
  in 
  Plateau's 
  experiments 
  on 
  

   figures 
  of 
  oil 
  in 
  dilute 
  alcohol, 
  was 
  about 
  two-thirds 
  filled 
  with 
  

   water, 
  and 
  a 
  black 
  cross 
  on 
  a 
  white 
  ground 
  was 
  seen 
  by 
  total 
  

   reflection 
  from 
  the 
  surface 
  of 
  the 
  water. 
  A 
  floating 
  disk 
  of 
  

   aluminum 
  was 
  moved 
  till 
  it 
  came 
  over 
  the 
  portion 
  of 
  the 
  water 
  

   from 
  which 
  the 
  reflection 
  had 
  taken 
  place. 
  The 
  reflection 
  

   was 
  destroyed 
  by 
  the 
  presence 
  of 
  the 
  disk 
  and 
  this 
  destruction 
  

   took 
  place 
  either 
  with 
  a 
  disk 
  whose 
  surface 
  was 
  partly 
  

   polished 
  or 
  with 
  a 
  disk 
  whose 
  under 
  surface 
  had 
  been 
  made 
  of 
  

   a 
  non-reflecting 
  grey 
  by 
  the 
  action 
  of 
  caustic 
  soda. 
  This 
  fact 
  

   is 
  interesting, 
  but 
  I 
  do 
  not 
  see 
  how 
  it 
  can 
  give 
  information 
  even 
  

   as 
  to 
  the 
  limiting 
  thickness 
  of 
  the 
  film 
  of 
  air 
  of 
  whose 
  conden- 
  

   sation 
  and 
  index 
  of 
  refraction 
  we 
  know 
  positively 
  nothing. 
  

  

  Stevens 
  Institute 
  of 
  Technology, 
  Mar. 
  1891. 
  

  

  