﻿Charge 
  of 
  the 
  Ions 
  emitted 
  lnj 
  Hot 
  Bodies. 
  749 
  

  

  condenser 
  allowed 
  to 
  flow 
  into 
  the 
  electrometer. 
  The 
  steady 
  

   deflexion 
  was 
  again 
  taken. 
  This 
  measures 
  the 
  total 
  number 
  

   of 
  ions 
  received 
  by 
  the 
  slit 
  and 
  the 
  plates 
  together. 
  This 
  is 
  

   only 
  true 
  of: 
  course 
  if 
  the 
  capacity 
  to 
  the 
  left 
  of 
  is 
  negligible 
  

   compared 
  with 
  that 
  to 
  the 
  right 
  of 
  E, 
  and 
  if 
  that 
  to 
  the 
  left 
  

   of 
  D 
  is 
  negligible 
  compared 
  with 
  that 
  to 
  the 
  right 
  of 
  F. 
  

   This 
  condition 
  was 
  always 
  fulfilled. 
  To 
  compare 
  the 
  number 
  

   of 
  ions 
  it 
  is 
  necessary 
  to 
  multiply 
  the 
  electrometer 
  deflexions 
  

   in 
  the 
  one 
  case 
  by 
  the 
  capacity 
  of 
  the 
  electrometer 
  and 
  in 
  

   the 
  other 
  by 
  the 
  combined 
  capacity 
  of 
  the 
  electrometer 
  and 
  the 
  

   condenser. 
  For 
  most 
  of 
  the 
  purposes 
  of 
  the 
  present 
  investi- 
  

   gation, 
  however, 
  the 
  ratio 
  of 
  the 
  two 
  deflexions 
  for 
  different 
  

   positions 
  of 
  the 
  slit 
  was 
  all 
  that 
  was 
  required. 
  

  

  In 
  an 
  investigation 
  of 
  this 
  kind 
  it 
  is 
  important 
  that 
  the 
  

   essential 
  parts 
  of 
  the 
  apparatus 
  should 
  be 
  easily 
  accessible, 
  

   so 
  that 
  any 
  desired 
  changes 
  may 
  be 
  readily 
  effected. 
  This 
  

   condition 
  was 
  satisfied 
  in 
  the 
  present 
  instance. 
  In 
  order 
  to 
  

   get 
  at 
  the 
  plates 
  and 
  strip 
  air 
  was 
  first 
  admitted 
  into 
  the 
  

   apparatus 
  by 
  means 
  of 
  a 
  glass 
  tap 
  connected 
  with 
  the 
  pump. 
  

   The 
  glass 
  tubes 
  were 
  cut 
  at 
  A 
  and 
  B 
  as 
  well 
  as 
  the 
  wires. 
  

   This 
  could 
  easily 
  be 
  done 
  time 
  after 
  time, 
  as 
  these 
  tubes 
  

   were 
  drawn 
  out 
  to 
  a 
  considerable 
  length, 
  much 
  greater 
  than 
  

   that 
  indicated 
  in 
  the 
  diagram, 
  at 
  the 
  ends. 
  The 
  tube 
  Q 
  

   could 
  then 
  be 
  lifted 
  off 
  from 
  the 
  stopper, 
  and 
  the 
  ebonite 
  

   frame 
  and 
  parts 
  that 
  it 
  supported 
  unscrewed 
  and 
  taken 
  

   away 
  for 
  alteration. 
  The 
  apparatus 
  could 
  be 
  replaced 
  with 
  

   equal 
  facility 
  ; 
  in 
  doing 
  so 
  it 
  was 
  necessary 
  to 
  pull 
  the 
  

   wires 
  connected 
  to 
  k 
  and 
  I 
  through 
  the 
  tubes 
  A 
  and 
  B 
  

   by 
  means 
  of 
  thin 
  wires 
  previously 
  threaded 
  through 
  these 
  

   tubes. 
  

  

  It 
  will 
  be 
  noticed 
  that, 
  with 
  the 
  device 
  which 
  has 
  been 
  

   described, 
  the 
  leaks 
  to 
  the 
  plate 
  and 
  through 
  the 
  slit 
  were 
  

   always 
  measured 
  simultaneously. 
  In 
  this 
  way 
  errors 
  arising 
  

   from 
  changes 
  in 
  the 
  magnitude 
  of 
  the 
  ionization 
  were 
  

   entirely 
  avoided. 
  This 
  is 
  a 
  matter 
  of 
  great 
  importance 
  in 
  

   dealing 
  with 
  an 
  effect 
  so 
  sensitive 
  to 
  small 
  changes 
  as 
  the 
  

   ionization 
  from 
  hot 
  bodies. 
  Although 
  it 
  was 
  not 
  perhaps 
  

   necessary, 
  the 
  temperature 
  was 
  kept 
  as 
  constant 
  as 
  possible 
  

   by 
  regulating 
  the 
  heating 
  current 
  to 
  a 
  constant 
  value. 
  This 
  

   is 
  a 
  satisfactory 
  method 
  when 
  the 
  pressure 
  of 
  the 
  gas 
  is 
  very 
  

   low. 
  Experiments 
  were 
  made 
  at 
  different 
  times 
  over 
  most 
  

   of 
  the 
  range 
  from 
  750° 
  C. 
  to 
  1200° 
  C. 
  

  

  The 
  magnetic 
  fields 
  were 
  furnished 
  by 
  a 
  large 
  electro- 
  

   magnet 
  which 
  was 
  capable, 
  with 
  a 
  gap 
  of 
  about 
  2 
  cms., 
  of 
  

   giving 
  a 
  very 
  uniform 
  field 
  of 
  up 
  to 
  5000 
  lines, 
  over 
  an 
  area 
  

   of 
  about 
  4 
  sq. 
  cms. 
  The 
  field 
  probably 
  did 
  not 
  vary 
  5 
  per 
  

  

  