﻿The 
  Absolute 
  Thermal 
  Conductivity 
  of 
  Glass. 
  599 
  

  

  plates. 
  Since 
  the 
  flow 
  o£ 
  heat 
  takes 
  place 
  in 
  a 
  direction 
  

   perpendicular 
  to 
  the 
  surface 
  of 
  this 
  film 
  of 
  foreign 
  matter, 
  

   the 
  presence 
  of 
  the 
  latter 
  must 
  introduce 
  a 
  thermal 
  resistance 
  

   which 
  is 
  uncertain 
  and 
  difficult 
  to 
  eliminate. 
  This 
  is 
  a 
  

   serious 
  objection 
  to 
  the 
  method 
  when 
  an 
  exact 
  determination 
  

   of 
  the 
  absolute 
  thermal 
  conductivity 
  is 
  required. 
  

  

  It 
  has 
  occurred 
  to 
  the 
  writer 
  that 
  this 
  difficulty 
  may 
  be 
  

   surmounted 
  in 
  certain 
  cases 
  by 
  having 
  the 
  substance 
  under 
  

   test 
  in 
  the 
  form 
  of 
  a 
  hollow 
  cylinder 
  containing 
  a 
  mercury 
  

   column. 
  The 
  heat 
  energy 
  generated 
  by 
  passing 
  an 
  electric 
  

   current 
  through 
  the 
  mercury 
  column 
  is 
  easily 
  measured, 
  and 
  

   the 
  mercury 
  in 
  the 
  tube 
  makes 
  good 
  thermal 
  contact 
  with 
  

   the 
  inner 
  surface 
  of 
  the 
  cylinder, 
  while 
  running 
  water 
  makes 
  

   good 
  contact 
  with 
  the 
  outer 
  surface. 
  

  

  § 
  3. 
  The 
  experiments 
  about 
  to 
  be 
  described 
  were 
  carried 
  

   out 
  on 
  the 
  lines 
  indicated 
  in 
  the 
  latter 
  half 
  of 
  § 
  2, 
  and 
  were 
  

   undertaken 
  with 
  the 
  object 
  of 
  determining 
  the 
  thermal 
  and 
  

   electrical 
  conductivities 
  of 
  glass 
  and 
  quartz. 
  

  

  Fig. 
  1. 
  

   E 
  

  

  B 
  

  

  B 
  

  

  A 
  capillary 
  tube 
  AA^ 
  fitted 
  at 
  each 
  end 
  with 
  wide 
  tubes 
  

   AF 
  and 
  AxGr 
  bent 
  at 
  right 
  angles 
  to 
  AA 
  l5 
  is 
  filled 
  with 
  

   mercury, 
  and 
  electrodes 
  are 
  inserted 
  into 
  the 
  mercury 
  in 
  the 
  

   tubes 
  AF 
  and 
  A 
  X 
  G. 
  By 
  means 
  of 
  these 
  electrodes 
  a 
  steady 
  

   electric 
  current 
  can 
  be 
  passed 
  through 
  the 
  mercury 
  column 
  

   AA 
  X 
  . 
  In 
  the 
  cylindrical 
  portions 
  BC 
  and 
  BiCj, 
  the 
  heat 
  

   generated 
  by 
  the 
  electric 
  current 
  flows 
  radially 
  through 
  the 
  

   cylinder 
  and 
  the 
  quantity 
  of 
  heat 
  flowing 
  through 
  per 
  

   second 
  is 
  easily 
  calculated. 
  In 
  order 
  to 
  eliminate 
  any 
  dis- 
  

   turbing 
  effects 
  at 
  the 
  ends 
  of 
  the 
  cylinder 
  considered 
  it 
  is 
  

   better 
  to 
  make 
  the 
  calculation 
  differentially. 
  

  

  2S2 
  

  

  