﻿400 
  Prof. 
  R. 
  W. 
  Wood 
  on 
  the 
  Electrical 
  Resonance 
  of 
  

  

  in 
  some 
  detail 
  the 
  manner 
  of 
  preparing 
  and 
  filling 
  the 
  bulbs. 
  

   It 
  is 
  in 
  the 
  first 
  place 
  a 
  great 
  economy 
  of 
  time 
  if 
  a 
  number 
  

   are 
  exhausted 
  at 
  once. 
  To 
  accomplish 
  this 
  I 
  have 
  fitted 
  the 
  

   mercurial 
  pump 
  with 
  a 
  glass 
  tube 
  having 
  half-a-dozen 
  lateral 
  

   branches 
  drawn 
  down 
  as 
  shown 
  in 
  fig. 
  1. 
  The 
  bulbs 
  are 
  

  

  Fig- 
  1. 
  

  

  blown 
  of 
  the 
  form 
  shown 
  in 
  the 
  same 
  figure, 
  and 
  a 
  piece 
  of 
  

   sodium 
  or 
  potassium 
  is 
  cut 
  up 
  under 
  ligroin 
  into 
  blocks 
  about 
  

   3 
  mm. 
  on 
  each 
  edge. 
  These 
  are 
  introduced 
  into 
  the 
  bulbs 
  as 
  

   quickly 
  as 
  possible 
  after 
  wiping 
  off 
  the 
  fluid, 
  and 
  the 
  stems 
  

   of 
  the 
  bulbs 
  drawn 
  down 
  to 
  a 
  small 
  bore 
  for 
  subsequent 
  

   sealing. 
  

  

  They 
  are 
  quickly 
  fastened 
  to 
  the 
  branch 
  tubes 
  and 
  exhausted. 
  

   I 
  find 
  it 
  a 
  good 
  plan 
  to 
  heat 
  the 
  metal 
  until 
  it 
  fuses 
  while 
  

   the 
  bulb 
  is 
  still 
  on 
  the 
  pump 
  ; 
  the 
  whole 
  bulb 
  may 
  be 
  warmed 
  

   by 
  a 
  Bunsen 
  flame 
  to 
  drive 
  off 
  absorbed 
  air. 
  If 
  the 
  exhaustion 
  

   is 
  carried 
  down 
  to 
  the 
  point 
  where 
  the 
  mercury 
  begins 
  to 
  

   hammer, 
  it 
  is 
  generally 
  sufficient. 
  The 
  bulbs 
  are 
  now 
  sealed 
  

   off 
  from 
  the 
  pump, 
  and 
  may 
  be 
  put 
  away 
  for 
  future 
  use, 
  or 
  

   experimented 
  with 
  at 
  once. 
  A 
  burner 
  should 
  be 
  made 
  by 
  

   drawing 
  out 
  a 
  glass 
  tube, 
  which 
  will 
  give 
  a 
  pointed 
  flame 
  

   about 
  half 
  a 
  centimetre 
  high, 
  and 
  the 
  tip 
  of 
  the 
  flame 
  allowed 
  

   to 
  play 
  against 
  the 
  spot 
  on 
  the 
  bulb 
  where 
  the 
  metal 
  lies 
  

   (fig. 
  l,a). 
  Sometimes 
  the 
  whole 
  bulb 
  will 
  suddenly 
  flash 
  a 
  

   deep 
  violet 
  or 
  blue, 
  and 
  sometimes 
  the 
  film 
  will 
  develop 
  

   more 
  slowly. 
  A 
  chain 
  of 
  three 
  or 
  four 
  bulbs 
  may 
  be 
  made, 
  

   the 
  sodium 
  heated 
  in 
  one, 
  and 
  the 
  clean 
  molten 
  metal 
  shaken 
  

   into 
  the 
  others, 
  drops 
  of 
  various 
  sizes 
  sticking 
  to 
  the 
  bulbs. 
  

   Coloured 
  films 
  can 
  then 
  be 
  formed 
  by 
  heating 
  these 
  clean 
  

   drops 
  in 
  the 
  bulbs. 
  This 
  shows 
  that 
  the 
  oxide 
  present 
  in 
  the 
  

   first 
  lump 
  has 
  nothing 
  to 
  do 
  with 
  the 
  production 
  of 
  the 
  colour. 
  

  

  I 
  shall 
  now 
  take 
  up 
  in 
  order 
  and 
  in 
  some 
  detail 
  the 
  

  

  