﻿84 
  Scientific 
  Intelligence. 
  

  

  then 
  strike 
  the 
  spherical 
  surface 
  obliquely 
  at 
  the 
  other 
  end 
  

   of 
  the 
  chord. 
  To 
  prevent 
  condensation 
  the 
  region 
  of 
  reflection 
  

   was 
  kept 
  warm 
  by 
  means 
  of 
  an 
  electrically 
  heated 
  metal 
  trough 
  

   the 
  lower 
  end 
  of 
  which 
  fitted 
  the 
  outside 
  of 
  the 
  glass 
  bulb 
  very 
  

   closely. 
  The 
  temperature 
  of 
  the 
  water 
  in 
  the 
  trough 
  was 
  main- 
  

   tained 
  at 
  30° 
  C. 
  so 
  that 
  the 
  temperature 
  of 
  the 
  glass 
  reflecting 
  

   surface 
  was 
  probably 
  between 
  0° 
  and 
  20°. 
  Below 
  the 
  zone 
  of 
  

   contact 
  of 
  the 
  heating 
  trough 
  the 
  rest 
  of 
  the 
  bulb 
  and 
  a 
  portion 
  

   of 
  the 
  auxiliary 
  apparatus 
  were 
  kept 
  immersed 
  in 
  liquid 
  oxygen. 
  

   This 
  liquid 
  was 
  contained 
  in 
  a 
  glass 
  vessel 
  with 
  unsilvered 
  walls 
  

   to 
  enable 
  the 
  making 
  of 
  visual 
  observations 
  without 
  changing 
  the 
  

   temperature 
  of 
  the 
  bulb 
  and 
  its 
  accessories. 
  

  

  When 
  the 
  mercury 
  in 
  the 
  auxiliary 
  system 
  had 
  been 
  warmed 
  

   for 
  a 
  very 
  short 
  time 
  the 
  layer 
  of 
  condensed 
  mercury 
  on 
  the 
  walls 
  

   of 
  the 
  inlet 
  tube 
  became 
  completely 
  opaque 
  and, 
  after 
  a 
  few 
  min- 
  

   utes, 
  the 
  condensed 
  vapor 
  in 
  the 
  bulb 
  became 
  visible. 
  The 
  layer 
  

   in 
  the 
  bulb 
  appeared 
  to 
  be 
  uniformly 
  distributed 
  from 
  the 
  instant 
  

   when 
  it 
  first 
  became 
  discernible 
  until 
  it 
  had 
  attained 
  almost 
  com- 
  

   plete 
  opacity. 
  "It 
  was 
  not 
  possible 
  to 
  detect 
  anywhere 
  a 
  struc- 
  

   ture 
  or 
  a 
  difference 
  in 
  transmissive 
  or 
  reflective 
  power, 
  save 
  at 
  a 
  

   zone 
  about 
  l 
  mm 
  wide 
  which 
  surrounded 
  the 
  heating 
  vessel 
  and 
  

   which 
  remained 
  absolutely 
  clear 
  and 
  transparent." 
  After 
  the 
  

   experiment 
  had 
  continued 
  for 
  " 
  a 
  good 
  20 
  minutes" 
  the 
  mercury 
  

   deposit 
  was 
  so 
  dense 
  that 
  an 
  incandescent 
  lamp 
  could 
  barely 
  be 
  

   seen 
  through 
  it. 
  The 
  heating 
  currents 
  were 
  then 
  broken, 
  the 
  

   liquid 
  oxygen 
  and 
  frost 
  removed, 
  air 
  was 
  admitted 
  to 
  the 
  bulb, 
  

   and 
  the 
  apparatus 
  was 
  allowed 
  to 
  come 
  to 
  room 
  temperature. 
  

   The 
  film 
  of 
  mercury, 
  now 
  liquid, 
  had 
  a 
  very 
  characteristic 
  and 
  

   uniform 
  opalescence. 
  At 
  the 
  expiration 
  of 
  24 
  hours 
  the 
  diffrac- 
  

   tion 
  rings 
  formed 
  by 
  the 
  mercury 
  droplets, 
  when 
  the 
  bulb 
  was 
  

   illuminated 
  by 
  a 
  distant 
  electric 
  light, 
  were 
  examined 
  and 
  found 
  

   to 
  have 
  the 
  same 
  appearance 
  for 
  all 
  parts 
  of 
  the 
  bulb 
  which 
  had 
  

   been 
  previously 
  frozen. 
  

  

  In 
  order 
  to 
  obtain 
  quantitative 
  measurements 
  the 
  experiment 
  

   was 
  repeated 
  and 
  continued 
  until 
  a 
  thicker 
  deposit 
  of 
  mercury 
  

   had 
  formed. 
  By 
  skilfully 
  manipulating 
  the 
  bulb 
  the 
  mercury 
  

   layer 
  was 
  collected 
  from 
  definite 
  spherical 
  zones 
  by 
  causing 
  an 
  

   auxiliary 
  globule 
  to 
  run 
  around 
  over 
  the 
  region 
  in 
  question. 
  B} 
  r 
  

   weighing 
  the 
  mercury 
  and 
  measuring 
  the 
  corresponding 
  areas 
  the 
  

   surface 
  density 
  of 
  the 
  selected 
  regions 
  was 
  obtained 
  directly. 
  The 
  

   zones 
  were 
  chosen 
  at 
  such 
  azimuths, 
  with 
  respect 
  to 
  the 
  direction 
  

   of 
  the 
  incident 
  stream 
  of 
  mercury 
  vapor 
  and 
  the 
  warmed 
  spot, 
  as 
  

   might 
  be 
  expected 
  to 
  produce 
  the 
  greatest 
  differences 
  in 
  surface 
  

   density 
  in 
  case 
  the 
  cosine 
  law 
  did 
  not 
  hold 
  true. 
  The 
  numbers 
  

   found, 
  however, 
  were 
  constant 
  within 
  the 
  limits 
  of 
  experimental 
  

   error. 
  Consequently 
  the 
  cosine 
  law 
  is 
  valid 
  even 
  when 
  there 
  is 
  

   no 
  temperature 
  equilibrium, 
  for 
  the 
  temperature 
  of 
  the 
  reflecting 
  

   surface 
  was 
  below 
  20° 
  C. 
  while 
  that 
  of 
  the 
  incident 
  mercury 
  vapor 
  

   was 
  above 
  80°. 
  — 
  Ann. 
  d. 
  Physik, 
  vol. 
  xlviii, 
  p. 
  1113, 
  Feb., 
  1916. 
  

  

  H. 
  S. 
  IT. 
  

  

  