﻿412 
  Dr. 
  Hodgson 
  and 
  Mr. 
  Mainstone 
  on 
  Heating 
  

  

  as 
  to 
  admit 
  the 
  bulb 
  of 
  a 
  sensitive 
  mercury 
  thermometer. 
  

   The 
  thermometer 
  was 
  completely 
  enclosed 
  in 
  the 
  tube 
  B, 
  the 
  

   open 
  end 
  of 
  which 
  was 
  closed 
  by 
  a 
  glass 
  cap 
  C, 
  and 
  rendered 
  

   airtight 
  by 
  means 
  of 
  picein. 
  A 
  line 
  wire, 
  which 
  was 
  soldered 
  

   to 
  the 
  cathode, 
  passed 
  along 
  the 
  tube 
  B, 
  and 
  enabled 
  elec- 
  

   trical 
  connexion 
  with 
  the 
  cathode 
  to 
  be 
  made. 
  The 
  diameter 
  

   of 
  the 
  tube 
  was 
  about 
  5 
  cm., 
  and 
  the 
  distance 
  separating 
  the 
  

   electrodes 
  14 
  cm. 
  

  

  In 
  some 
  later 
  experiments 
  a 
  tube 
  of 
  the 
  form 
  shown 
  in 
  

   fig. 
  2 
  was 
  used. 
  

  

  Fin-. 
  2. 
  

  

  This 
  consisted 
  of 
  two 
  spherical 
  bulbs 
  each 
  11 
  cm. 
  in 
  

   diameter, 
  in 
  each 
  of 
  which 
  could 
  be 
  fixed 
  an 
  electrode 
  

   similar 
  to 
  the 
  cathode 
  of 
  fig. 
  1. 
  The 
  thermometers 
  were 
  

   entirely 
  enclosed 
  in 
  the 
  vacuum-tube, 
  and 
  the 
  leads 
  in 
  this 
  

   case 
  passed 
  through 
  glass 
  tubes 
  in 
  order 
  to 
  confine 
  the 
  

   discharge 
  to 
  the 
  electrode 
  proper. 
  With 
  this 
  form 
  of 
  

   apparatus 
  there 
  were 
  two 
  distinct 
  advantages 
  : 
  firstly, 
  the 
  

   electrodes 
  were 
  fixed 
  at 
  some 
  distance 
  from 
  the 
  sides 
  of 
  the 
  

   vacuum 
  vessel, 
  and 
  so 
  electrostatic 
  disturbances 
  of 
  the 
  field 
  

   near 
  the 
  cathode 
  were 
  avoided; 
  and 
  secondly, 
  the 
  whole 
  

   could 
  be 
  immersed 
  in 
  a 
  water-bath, 
  which 
  allowed 
  a 
  more 
  

   accurate 
  observation 
  of 
  the 
  equilibrium 
  temperature 
  to 
  be 
  

   made. 
  The 
  heat 
  capacity 
  of 
  the 
  cathode 
  complete 
  with 
  

   thermometer 
  and 
  leads 
  was 
  obtained 
  experimentally, 
  using 
  

   a 
  modified 
  form 
  of 
  Regnault's 
  specific 
  heat 
  apparatus. 
  

  

  