﻿970 
  Mr. 
  R. 
  W. 
  Lawson 
  on 
  the 
  Spectra 
  of 
  

  

  the 
  electrical 
  apparatus. 
  The 
  arc-deflecting 
  electromagnet 
  

   has 
  been 
  omitted 
  from 
  the 
  diagram 
  of 
  the 
  generator, 
  as 
  its 
  

   omission 
  simplifies 
  the 
  diagram. 
  AA 
  are 
  air-cored 
  choking 
  

   coils 
  for 
  the 
  purpose 
  of 
  preventing 
  the 
  oscillations 
  from 
  

   reacting 
  on 
  the 
  primary 
  supply 
  circuit; 
  BB 
  are 
  block 
  con- 
  

   densers; 
  C 
  a 
  variable 
  capacity 
  in 
  the 
  form 
  of 
  oil 
  condensers; 
  

   and 
  D 
  is 
  a 
  variable 
  primary 
  inductance. 
  The 
  Oudin 
  coil 
  E 
  

   was 
  of 
  about 
  one 
  metre 
  in 
  length, 
  and 
  consisted 
  of 
  some 
  

   2100 
  turns 
  of 
  fine 
  copper 
  wire 
  wrapped 
  on 
  glass 
  tubing 
  of 
  

   3'4 
  cm. 
  diameter. 
  It 
  served 
  to 
  cut 
  down 
  the 
  current 
  in 
  

   many 
  of 
  the 
  high-energy 
  discharges, 
  and 
  thus 
  prevented 
  

   undue 
  heating 
  in 
  the 
  Geissler 
  tube. 
  After 
  passing 
  through 
  

   the 
  discharge 
  tube 
  the 
  current 
  passed 
  across 
  the 
  thermo- 
  

   electric 
  junction 
  shown, 
  and 
  thus 
  only 
  the 
  portion 
  of 
  the 
  

   current 
  traversing 
  the 
  tube 
  was 
  registered. 
  V 
  is 
  an 
  electro- 
  

   static 
  voltmeter 
  arranged 
  as 
  shown. 
  With 
  lower-frequency 
  

   discharges 
  of 
  the 
  order 
  of 
  2 
  x 
  10 
  5 
  per 
  second 
  the 
  energy 
  in 
  

   the 
  oscillating 
  circuit 
  was 
  of 
  a 
  very 
  high 
  order 
  quantitatively, 
  

   and 
  it 
  was 
  a 
  very 
  easy 
  matter 
  to 
  draw 
  from 
  the 
  coil 
  D 
  an 
  

   arc 
  of 
  two 
  or 
  three 
  inches 
  in 
  length. 
  With 
  discharges 
  of 
  

   such 
  frequency 
  it 
  was 
  found 
  possible 
  to 
  boil 
  the 
  mercury 
  in 
  

   the 
  upper 
  cup 
  of 
  the 
  discharge 
  tube, 
  owing 
  to 
  the 
  large 
  

   current 
  passing 
  and 
  the 
  heat 
  produced 
  where 
  the 
  discharge 
  

   entered 
  the 
  tube. 
  For 
  this 
  reason 
  the 
  coil 
  E 
  was 
  usually 
  

   inserted, 
  and 
  found 
  to 
  produce 
  more 
  satisfactory 
  working. 
  

   With 
  higher 
  frequencies 
  it 
  could 
  usually 
  be 
  dispensed 
  with, 
  

   as 
  the 
  energy 
  was 
  not 
  then 
  so 
  great. 
  The 
  maximum 
  

   frequency 
  used 
  was 
  about 
  1*5 
  x 
  10 
  6 
  per 
  second, 
  whilst 
  

   0'22 
  x 
  10 
  6 
  was 
  the 
  lowest 
  frequency 
  attainable 
  in 
  the 
  present 
  

   experiments. 
  

  

  Fig. 
  3. 
  

  

  & 
  

  

  (b) 
  The 
  second 
  arrangement 
  used 
  was 
  simply 
  an 
  adaptation 
  

   of 
  the 
  wave-meter, 
  and 
  will 
  be 
  clearly 
  understood 
  from 
  fig. 
  3. 
  

   The 
  wave-meter 
  inductance 
  A 
  consisted 
  of 
  a 
  circular 
  coil 
  of 
  

  

  