﻿380 
  Scientific 
  Intelligence. 
  

  

  singular 
  manner 
  in 
  which 
  these 
  rays 
  behave 
  with 
  regard 
  to 
  ab- 
  

   sorption, 
  as 
  we 
  have 
  pointed 
  out 
  in 
  a 
  recent 
  article, 
  would 
  seem 
  

   to 
  confirm 
  the 
  idea. 
  

  

  Will 
  this 
  collection 
  of 
  well-grounded 
  ideas 
  remove 
  the 
  last 
  dif- 
  

   ficulties 
  ? 
  To 
  affirm 
  this 
  would 
  be 
  to 
  proceed 
  too 
  quickly, 
  since 
  

   the 
  cause 
  of 
  the 
  bombardment 
  is 
  not 
  yet 
  apparent 
  to 
  us. 
  In 
  any 
  

   case 
  the 
  first 
  objection 
  which 
  comes 
  to 
  our 
  minds, 
  that 
  of 
  a 
  neces- 
  

   sary 
  loss 
  of 
  mass 
  of 
  the 
  radium, 
  will 
  not 
  stand 
  examination, 
  for, 
  

   as 
  has 
  been 
  shown 
  by 
  M. 
  Curie, 
  the 
  charges 
  carried 
  off 
  are 
  so 
  

   feeble, 
  that 
  if 
  we 
  admit 
  the 
  same 
  proportions 
  as 
  with 
  cathodic 
  

   rays, 
  some 
  millions 
  of 
  years 
  would 
  be 
  required 
  to 
  remove 
  one 
  

   m. 
  grm. 
  in 
  the 
  case 
  of 
  the 
  most 
  intense 
  radiation 
  that 
  has 
  yet 
  been 
  

   observed. 
  

  

  What 
  can, 
  however, 
  be 
  said 
  with 
  certainty, 
  is 
  that 
  the 
  new 
  dis- 
  

   coveries 
  singularly 
  limit 
  the 
  field 
  for 
  hypotheses, 
  and 
  by 
  fixing 
  

   the 
  direction 
  for 
  research 
  permit 
  us 
  to 
  forsee 
  a 
  generalisation 
  of 
  

   great 
  magnitude 
  which 
  will 
  be 
  of 
  great 
  attraction 
  in 
  the 
  study 
  of 
  

   certain 
  properties 
  of 
  matter 
  to 
  which 
  in 
  the 
  last 
  few 
  years 
  a 
  large 
  

   body 
  of 
  scientific 
  men 
  have 
  turned. 
  — 
  Revue 
  Generate 
  des 
  Sciences, 
  

   No. 
  5, 
  March 
  15, 
  1900.— 
  Chem. 
  News, 
  lxxxi, 
  145. 
  

  

  4. 
  The 
  Echelon 
  Spectroscope 
  and 
  the 
  Zeeman 
  effect. 
  — 
  A 
  

   paper 
  by 
  Lord 
  Blythswood 
  and 
  Dr. 
  E. 
  W. 
  Makchant, 
  in 
  the 
  

   April 
  number 
  of 
  the 
  Philosophical 
  Magazine, 
  gives 
  an 
  interest- 
  

   ing 
  account 
  of 
  investigations 
  made 
  with 
  the 
  echelon 
  diffraction- 
  

   grating 
  invented 
  by 
  Professor 
  A. 
  A. 
  Michelson 
  (this 
  Journal, 
  

   v, 
  215, 
  1898). 
  It 
  shows 
  how 
  admirably 
  it 
  is 
  adapted, 
  as 
  early 
  

   pointed 
  out 
  by 
  the 
  inventor, 
  for 
  the 
  study 
  of 
  certain 
  phenomena, 
  

   e. 
  g. 
  the 
  Zeeman 
  effect. 
  The 
  grating 
  used 
  by 
  the 
  present 
  authors 
  

   was 
  by 
  Hilger 
  and 
  consisted 
  of 
  fifteen 
  plates, 
  each 
  about 
  j-5 
  mm 
  

   in 
  thickness, 
  made 
  of 
  light 
  flint 
  glass 
  and 
  set, 
  as 
  finally 
  arranged, 
  

   so 
  as 
  to 
  make 
  steps 
  -5 
  mm 
  wide. 
  This 
  was 
  combined 
  with 
  the 
  tel- 
  

   escope 
  and 
  collimator 
  of 
  a 
  large 
  goniometer, 
  the 
  telescopes 
  hav- 
  

   ing 
  object-glasses 
  of 
  twenty-eight 
  inch 
  focus 
  and 
  two 
  inch 
  aper- 
  

   ture. 
  A 
  small 
  solar 
  telescope 
  was 
  employed 
  to 
  obtain 
  the 
  neces- 
  

   sary 
  preliminary 
  dispersion. 
  The 
  methods 
  of 
  adjusting 
  the 
  

   instrument 
  are 
  described 
  in 
  detail, 
  and 
  also 
  the 
  values 
  deduced 
  

   for 
  the 
  constant 
  of 
  the 
  grating, 
  which 
  depends 
  for 
  its 
  value 
  upon 
  

   the 
  wave-length 
  of 
  light 
  and 
  the 
  refractive 
  index 
  of 
  the 
  glass 
  

   employed. 
  When 
  this 
  constant 
  is 
  known, 
  the 
  difference 
  in 
  wave- 
  

   length 
  between 
  two 
  lines 
  seen 
  in 
  the 
  echelon 
  may 
  be 
  determined 
  

   if 
  their 
  dispersion 
  relative 
  to 
  the 
  distance 
  between 
  two 
  successive 
  

   orders 
  is 
  known. 
  This 
  constant 
  is 
  independent 
  of 
  the 
  width 
  of 
  

   the 
  steps, 
  so 
  that 
  it 
  is 
  immaterial 
  how 
  they 
  are 
  put 
  together, 
  the 
  

   only 
  condition 
  being 
  that 
  the 
  instrument 
  shall 
  not 
  be 
  much 
  

   tilted 
  ; 
  or, 
  in 
  other 
  words, 
  that 
  the 
  light 
  shall 
  pass 
  through 
  in 
  a 
  

   direction 
  nearly 
  normal 
  to 
  the 
  plates. 
  A 
  large 
  magnet 
  was 
  

   employed, 
  giving 
  a 
  field 
  up 
  to 
  40,000 
  C. 
  G. 
  S. 
  units. 
  The 
  effects 
  

   especially 
  observed 
  were 
  those 
  for 
  the 
  blue 
  (4358) 
  and 
  green 
  

   (5460) 
  lines 
  of 
  the 
  mercury 
  spectrum. 
  Both 
  of 
  these 
  could 
  be 
  

   photographed, 
  the 
  former 
  requiring 
  an 
  exposure 
  of 
  from 
  ten 
  to 
  

  

  