﻿810 
  Mr. 
  PL 
  L. 
  P. 
  Jolly 
  on 
  the 
  

  

  The 
  results 
  indicated 
  by 
  Carve 
  3 
  (PL 
  XIV.) 
  are 
  not 
  vital 
  to 
  

   the 
  present 
  investigation, 
  but 
  were 
  obtained 
  as 
  a 
  test 
  of 
  the 
  

   electroscope 
  method 
  of 
  measuring 
  small 
  alternating 
  currents. 
  

   But 
  it 
  is 
  useful 
  to 
  know 
  at 
  what 
  pressures 
  one 
  must 
  guard 
  

   most 
  caref 
  ally 
  against 
  a 
  change 
  of 
  pressure 
  in 
  measuring 
  the 
  

   radiation 
  from 
  the 
  discharge. 
  

  

  Curves 
  4 
  and 
  5 
  are 
  important. 
  They 
  show 
  the 
  relation 
  

   between 
  the 
  total 
  radiation 
  in 
  the 
  visible 
  spectrum 
  and 
  the 
  

   current-density. 
  The 
  first 
  of 
  them 
  was 
  obtained 
  by 
  taking- 
  

   only 
  one 
  reading 
  for 
  each 
  point, 
  and 
  the 
  values 
  representing 
  

   intensity 
  of 
  the 
  radiation 
  are 
  liable 
  to 
  errors 
  whose 
  magnitude 
  

   can 
  be 
  gauged 
  from 
  the 
  curve. 
  Curve 
  5 
  is 
  a 
  similar 
  one 
  in 
  

   which 
  four 
  readings 
  went 
  to 
  each 
  point. 
  The 
  greater 
  regu- 
  

   larity 
  of 
  this 
  curve 
  is 
  to 
  be 
  attributed 
  not 
  only 
  to 
  the 
  more 
  

   numerous 
  observations, 
  but 
  also 
  to 
  the 
  lower 
  pressure 
  in 
  the 
  

   discharge-tube. 
  There 
  seems 
  little 
  room 
  for 
  doubt 
  that 
  up 
  to 
  

   the 
  current-density 
  observed 
  (about 
  100 
  m.a. 
  per 
  sq. 
  mm.), 
  

   the 
  energy 
  of 
  total 
  visible 
  radiation, 
  and 
  therefore 
  of 
  any 
  

   given 
  line, 
  varies 
  directly 
  as 
  the 
  current-density. 
  Under 
  

   these 
  circumstances 
  there 
  would 
  be 
  little 
  gain 
  in 
  examining 
  

   single 
  lines 
  with 
  a 
  view 
  to 
  proving 
  the 
  same 
  proportionality 
  

   in 
  their 
  case, 
  and 
  we 
  proceed 
  with 
  the 
  investigation 
  of 
  con- 
  

   densed 
  discharges. 
  

  

  B. 
  Displacement 
  of 
  Energy 
  in 
  the 
  Spectrum, 
  

  

  Obviously, 
  from 
  the 
  smallness 
  of 
  the 
  deflexions 
  obtained 
  

   in 
  the 
  above 
  curve, 
  we 
  must 
  have 
  a 
  stronger 
  source 
  of 
  energy 
  

   if 
  any 
  spectroscopic 
  separation 
  is 
  to 
  take 
  place. 
  The 
  only 
  

   possible 
  way 
  is 
  to 
  examine 
  the 
  spectrum 
  of 
  the 
  condensed 
  

   discharge. 
  

  

  So 
  far 
  our 
  observations 
  have 
  been 
  concerned 
  with 
  the 
  

   steady 
  discharges 
  produced 
  by 
  the 
  alternator 
  alone, 
  and 
  

   although 
  the 
  discharge-tube 
  was 
  placed 
  close 
  up 
  to 
  the 
  slit 
  

   of 
  the 
  spectrometer, 
  there 
  were 
  no 
  disturbances 
  of 
  the 
  

   galvanometer 
  due 
  to 
  the 
  turning 
  on 
  of 
  the 
  current. 
  (It 
  

   should 
  be 
  explained 
  that 
  the 
  only 
  possible 
  method 
  of 
  ob- 
  

   serving 
  was 
  to 
  watch 
  the 
  galvanometer 
  when 
  the 
  current 
  

   was 
  suddenly 
  put 
  on, 
  as 
  the 
  heating 
  would 
  be 
  too 
  great 
  if 
  

   the 
  current 
  were 
  allowed 
  to 
  run 
  continuously 
  and 
  a 
  shutter 
  

   opened 
  when 
  desired.) 
  Unfortunately 
  the 
  disruptive 
  dis- 
  

   charge 
  caused 
  a 
  marked 
  disturbance 
  in 
  the 
  suspended 
  system 
  

   of 
  the 
  galvanometer, 
  and 
  it 
  became 
  necessary 
  to 
  investigate 
  

   carefully 
  the 
  magnitude 
  and 
  constancy 
  of 
  these 
  spurious 
  

   deflexions. 
  The 
  sum-total 
  of 
  the 
  disturbing 
  effects 
  may 
  be 
  

   stated 
  as 
  follows 
  : 
  — 
  

  

  