﻿Chemistry 
  and 
  Physics. 
  153 
  

  

  12. 
  " 
  On 
  the 
  Photographic 
  Spectrum 
  of 
  the 
  Great 
  Nebula 
  in 
  

   Orion" 
  by 
  J. 
  Norman 
  Lockyer, 
  C.B., 
  F.R.S. 
  Abstract 
  from 
  

  

  the 
  Proc. 
  Hoy. 
  Soc, 
  lvi., 
  285. 
  — 
  The 
  paper 
  consists 
  of 
  a 
  descrip- 
  

   tion 
  and 
  discussion 
  of 
  photographs 
  of 
  the 
  spectrum 
  of 
  the 
  Orion 
  

   Nebula, 
  taken 
  with 
  the 
  30 
  inch 
  reflector 
  at 
  Westgate-on-Sea 
  in 
  

   February, 
  1890, 
  of 
  which 
  a 
  preliminary 
  account 
  was 
  communicated 
  

   to 
  the 
  Royal 
  Society 
  at 
  the 
  time. 
  Fifty-four 
  lines 
  are 
  tabulated 
  

   as 
  belonging 
  to 
  the 
  spectrum 
  of 
  the 
  nebula, 
  nine 
  of 
  them 
  being 
  

   due 
  to 
  hydrogen. 
  The 
  complete 
  discussion 
  has 
  led 
  to 
  the 
  follow- 
  

   ing 
  general 
  conclusions: 
  — 
  

  

  1. 
  The 
  spectrum 
  of 
  the 
  nebula 
  of 
  Orion 
  is 
  a 
  compound 
  one 
  con- 
  

   sisting 
  of 
  hydrogen 
  lines, 
  low 
  temperature 
  metallic 
  lines 
  and 
  flut- 
  

   ings, 
  and 
  high 
  temperature 
  lines. 
  The 
  mean 
  temperature, 
  how- 
  

   ever, 
  is 
  relatively 
  low.* 
  

  

  2. 
  The 
  spectrum 
  is 
  different 
  in 
  different 
  parts 
  of 
  the 
  nebula. 
  

  

  3. 
  The 
  spectrum 
  bears 
  a 
  striking 
  resemblance 
  to 
  that 
  of 
  the 
  

   planetary 
  nebulas 
  and 
  bright 
  line 
  stars. 
  , 
  

  

  4. 
  The 
  suggestion, 
  therefore, 
  that 
  these 
  are 
  bodies 
  which 
  must 
  

   be 
  closely 
  associated 
  in 
  any 
  valid 
  scheme 
  of 
  classification, 
  is 
  con- 
  

   firmed. 
  

  

  5. 
  Many 
  of 
  the 
  lines 
  which 
  appear 
  bright 
  in 
  the 
  spectrum 
  of 
  

   the 
  nebula 
  appear 
  dark 
  in 
  the 
  spectra 
  of 
  stars 
  of 
  Groups 
  II 
  and 
  III 
  ; 
  

   and 
  in 
  the 
  earlier 
  stars 
  of 
  Group 
  IV, 
  and 
  a 
  gradual 
  change 
  from 
  

   bright 
  to 
  dark 
  lines 
  has 
  been 
  found. 
  

  

  6. 
  The 
  view, 
  therefore, 
  that 
  bright 
  line 
  stars 
  occupy 
  an 
  inter- 
  

   mediate 
  position 
  between 
  nebulae 
  and 
  stars 
  of 
  Groups 
  II 
  and 
  III 
  is 
  

   greatly 
  strengthened 
  by 
  these 
  researches. 
  

  

  13. 
  Elementary 
  Lessons 
  in 
  Electricity 
  and 
  Magnetism 
  by 
  

   Silyanus 
  P. 
  Thompson. 
  New 
  edition, 
  revised 
  throughout 
  with 
  

   additions, 
  628 
  pp. 
  New 
  York 
  and 
  London, 
  1895 
  (Macmillan 
  & 
  

   Co.) 
  — 
  The 
  first 
  edition 
  of 
  Thompson's 
  Lessons, 
  published 
  in 
  1881, 
  

   is 
  well 
  known 
  as 
  one 
  of 
  the 
  best 
  elementary 
  books 
  on 
  Electricity 
  

   and 
  Magnetism 
  ever 
  presented 
  and, 
  with 
  later 
  reprints, 
  it 
  has 
  had 
  

   well 
  deserved 
  success. 
  The 
  present 
  new 
  edition 
  contains 
  all 
  the 
  

   good 
  features 
  of 
  the 
  earlier 
  ones, 
  while 
  the 
  large 
  amount 
  of 
  new 
  

   matter 
  added 
  makes 
  it 
  fresh 
  and 
  new 
  throughout. 
  Thus 
  for 
  ex- 
  

   ample, 
  to 
  the 
  subject 
  of 
  Electric 
  waves 
  a 
  special 
  chapter 
  is 
  devoted 
  

   in 
  which 
  the 
  work 
  of 
  Hertz 
  and 
  others 
  is 
  clearly, 
  if 
  briefly, 
  pre- 
  

   sented. 
  Many 
  new 
  illustrations 
  are 
  introduced 
  ; 
  these 
  represent- 
  

   ing 
  the 
  lines 
  of 
  force 
  in 
  various 
  electric 
  fields, 
  e. 
  g. 
  in 
  electrostatic 
  

   induction, 
  etc., 
  will 
  be 
  particularly 
  helpful 
  to 
  the 
  student. 
  The 
  

   work 
  in 
  its 
  present 
  form 
  deserves 
  high 
  commendation. 
  A 
  

   criticism 
  might 
  be 
  offered 
  by 
  the 
  teacher 
  using 
  the 
  book 
  to 
  the 
  

   arrangement 
  of 
  matter 
  in 
  some 
  cases, 
  but 
  there 
  may 
  be 
  room 
  

   here 
  for 
  some 
  difference 
  of 
  opinion. 
  v 
  

  

  *Roy. 
  Soc. 
  Proc, 
  vol. 
  xliii, 
  p. 
  152, 
  1887. 
  

  

  