﻿Chemistry 
  and 
  Physics. 
  295 
  

  

  "The 
  peculiar 
  interest 
  of 
  the 
  gases 
  argon 
  and 
  helium 
  is 
  in 
  their 
  

   monatomic 
  characters. 
  The 
  view 
  now 
  generally 
  taken 
  is 
  that 
  the 
  

   electric 
  discharge 
  is 
  conveyed 
  in 
  all 
  cases 
  by 
  ions, 
  these 
  ions 
  

   being 
  produced 
  h\ 
  a 
  dissociation 
  process 
  of 
  some 
  kind. 
  If 
  this 
  

   be 
  admitted 
  there 
  can 
  be 
  no 
  escape 
  from 
  the 
  conclusion 
  that 
  the 
  

   ions 
  of 
  monatomic 
  gases 
  are 
  split 
  up 
  into 
  something 
  smaller. 
  The 
  

   above 
  experiments 
  make 
  it 
  sufficiently 
  clear, 
  I 
  think, 
  that 
  these 
  

   gases 
  convey 
  the 
  discharge 
  in 
  a 
  normal 
  manner. 
  If 
  the 
  potential- 
  

   fall 
  at 
  the 
  cathode 
  is 
  a 
  measure 
  of 
  the 
  energy 
  expended 
  in 
  the 
  

   ionization 
  of 
  the 
  gas 
  when 
  effected 
  by 
  an 
  electric 
  field, 
  the 
  experi- 
  

   ments 
  show 
  that 
  the 
  ionization 
  of 
  argon 
  and 
  helium 
  is 
  somewhat 
  

   more 
  easily 
  effected 
  than 
  that 
  of 
  other 
  gases. 
  There 
  are 
  other 
  

   reasons 
  for 
  thinking 
  that 
  the 
  atomicity 
  of 
  an 
  elementary 
  gas 
  is 
  

   not 
  an 
  important 
  feature 
  in 
  its 
  facility 
  of 
  ionization. 
  Thus 
  mer- 
  

   cury 
  vapor 
  was 
  found 
  by 
  Thomson 
  and 
  Rutherford 
  to 
  conduct 
  

   much 
  more 
  lreely 
  than 
  air 
  under 
  the 
  influence 
  of 
  the 
  X-rays. 
  

   Helium, 
  on 
  the 
  other 
  hand, 
  conducts 
  only 
  about 
  half 
  as 
  well 
  as 
  

   air.— 
  Phil. 
  Mag., 
  March, 
  1900, 
  pp. 
  293-307. 
  J. 
  t. 
  

  

  9. 
  An 
  Experimental 
  Research 
  on 
  Some 
  Standards 
  of 
  Light 
  ; 
  by 
  

   J. 
  E. 
  Petavel. 
  — 
  The 
  author 
  has 
  carried 
  on, 
  during 
  the 
  past 
  

   three 
  years, 
  an 
  extensive 
  series 
  of 
  experiments, 
  having 
  as 
  their 
  

   object 
  the 
  investigation 
  of 
  the 
  most 
  valuable 
  light-standards 
  of 
  

   the 
  incandescent 
  type. 
  The 
  requirements 
  for 
  a 
  practical 
  stand- 
  

   ard 
  are 
  summarized 
  as 
  follows: 
  (l) 
  The 
  standard 
  must 
  remain 
  

   coustant 
  for 
  long 
  as 
  well 
  as 
  short 
  periods. 
  (2) 
  It 
  should 
  be 
  

   reproducible. 
  (3) 
  The 
  light 
  emitted 
  should 
  be 
  as 
  nearly 
  as 
  

   possible 
  of 
  the 
  same 
  spectral 
  composition 
  as 
  that 
  of 
  the 
  chief 
  

   artificial 
  lights 
  now 
  in 
  common 
  use. 
  

  

  Experiments 
  with 
  the 
  electric 
  arc 
  have 
  led 
  the 
  author 
  to 
  the 
  

   following 
  conclusions 
  : 
  

  

  (1.) 
  The 
  intrinsic 
  brilliancy 
  of 
  the 
  crater 
  of 
  a 
  silent 
  arc 
  is 
  

   about 
  147 
  candle-power 
  per 
  square 
  millimeter. 
  

  

  (2.) 
  Even 
  when 
  the 
  most 
  favorable 
  conditions 
  are 
  selected, 
  

   and 
  the 
  intensity 
  of 
  current 
  and 
  the 
  length 
  of 
  the 
  arc 
  are 
  

   maintained 
  constant, 
  it 
  is 
  difficult 
  to 
  obtain 
  consistent 
  results, 
  

   variations 
  of 
  over 
  5 
  per 
  cent, 
  being 
  by 
  no 
  means 
  unfrequent, 
  

   The 
  crater 
  of 
  the 
  arc 
  does 
  not, 
  therefore, 
  possess 
  the 
  qualities 
  

   required 
  of 
  a 
  standard. 
  

  

  (3.) 
  Variations 
  in 
  the 
  size 
  of 
  the 
  carbons, 
  in 
  the 
  intensity 
  and 
  

   density 
  of 
  the 
  current, 
  in 
  the 
  length 
  of 
  the 
  arc, 
  and 
  in 
  the 
  total 
  

   power 
  expended 
  ( 
  as 
  long 
  as 
  the 
  arc 
  is 
  kept 
  silent,) 
  will 
  not 
  cause 
  

   the 
  intrinsic 
  brilliancy 
  to 
  vary 
  more 
  than 
  10 
  per 
  cent, 
  on 
  either 
  

   side 
  of 
  the 
  mean. 
  

  

  (4.) 
  No 
  sensible 
  variation 
  in 
  the 
  intrinsic 
  brilliancy, 
  and 
  there- 
  

   fore 
  in 
  the 
  temperature 
  of 
  the 
  crater, 
  is 
  produced 
  by 
  placing 
  the 
  

   carbons 
  in 
  an 
  enclosure 
  maintained 
  at 
  over 
  900° 
  C. 
  

  

  The 
  experiments 
  confirm 
  the 
  theory 
  that 
  the 
  crater 
  of 
  the 
  arc 
  is 
  

   at 
  the 
  temperature 
  of 
  volatilization 
  of 
  carbon. 
  

  

  The 
  Lummer 
  and 
  Kurlbaum 
  incandescent 
  platinum 
  standard 
  

   was 
  also 
  made 
  the 
  object 
  of 
  careful 
  trials, 
  but 
  the 
  result 
  was 
  

  

  