﻿lis 
  Scientific 
  Intelligence. 
  

  

  solutions 
  and 
  alloys, 
  alloys 
  of 
  metals 
  with 
  carbides, 
  oxides 
  and 
  

   sulphides, 
  including 
  iron 
  and 
  steel, 
  mattes, 
  phase 
  rule, 
  metallur- 
  

   gical 
  reactions, 
  oxidation 
  and 
  reduction, 
  the 
  decomposition 
  of 
  

   carbon 
  monoxide, 
  blast-furnace 
  processes, 
  the 
  reactions 
  of 
  sul- 
  

   phides, 
  etc. 
  The 
  discussions 
  are 
  interesting 
  and 
  valuable 
  in 
  

   presenting 
  scientific 
  explanations 
  of 
  many 
  metallurgical 
  phe- 
  

   nomena, 
  h. 
  l. 
  w. 
  

  

  5. 
  The 
  Determination 
  of 
  Indices 
  of 
  Refraction 
  of 
  Transpar- 
  

   ent 
  Solids. 
  — 
  The 
  problem 
  of 
  decermining 
  the 
  indices 
  of 
  refrac- 
  

   tion, 
  for 
  monochromatic 
  light, 
  of 
  solid 
  specimens 
  having 
  surfaces 
  

   which 
  may 
  not 
  be 
  modified 
  or 
  which 
  are 
  unpolished 
  and 
  irreg- 
  

   ular 
  is 
  one 
  of 
  no 
  little 
  practical 
  importance 
  and 
  hence 
  it 
  has 
  

   been 
  attacked 
  and 
  more 
  or 
  less 
  satisfactorily 
  solved 
  in 
  late 
  

   years, 
  the 
  impetus 
  arising 
  largely 
  from 
  the 
  exigencies 
  of 
  the 
  

   world 
  war. 
  In 
  particular, 
  the 
  method 
  of 
  immersion 
  was 
  applied 
  

   in 
  an 
  excellent 
  manner 
  by 
  R. 
  W. 
  Cheshire 
  (see 
  42, 
  498, 
  1916). 
  

   The 
  most 
  recent, 
  and 
  apparently 
  the 
  most 
  promising, 
  develop- 
  

   ment 
  of 
  the 
  method 
  of 
  immersion 
  is 
  due 
  to 
  Ch. 
  Fabry. 
  This 
  

   investigator 
  calls 
  attention 
  to 
  two 
  significant 
  facts: 
  (a) 
  the 
  

   earlier 
  applications 
  of. 
  the 
  method 
  of 
  immersion 
  require 
  the 
  

   experimental 
  realization 
  of 
  exact 
  equality 
  between 
  the 
  indices 
  

   of 
  refraction 
  of 
  the 
  liquid 
  and 
  of 
  the 
  solid 
  under 
  investigation, 
  

   and 
  (b) 
  these 
  processes 
  usually 
  enable 
  the 
  determination 
  of 
  

   only 
  a 
  few 
  units 
  in 
  the 
  fourth 
  decimal 
  place 
  to 
  be 
  made, 
  whereas 
  

   many 
  of 
  the 
  computations 
  of 
  geometrical 
  optics 
  require 
  for 
  

   their 
  adequate 
  solution 
  a 
  knowledge 
  of 
  one 
  or 
  two 
  units 
  in 
  the 
  

   fifth 
  place 
  of 
  decimals. 
  Fabry's 
  development 
  fulfills 
  the 
  last 
  

   requirement 
  and 
  therefore 
  it 
  seems 
  desirable 
  to 
  give 
  a 
  brief 
  

   account 
  of 
  it 
  in 
  this 
  place. 
  

  

  The 
  basic 
  idea 
  is 
  to 
  use 
  a 
  differential 
  method 
  involving 
  inter- 
  

   polation 
  within 
  narrow 
  ranges 
  of 
  angular 
  deviation. 
  Some 
  of 
  

   the 
  advantages 
  thus 
  obtained 
  are 
  (a) 
  saving 
  of 
  time 
  as 
  a 
  conse- 
  

   quence 
  of 
  not 
  having 
  to 
  attain 
  exact 
  equality 
  of 
  the 
  indices 
  of 
  

   refraction 
  of 
  the 
  immersion 
  liquid 
  and 
  the 
  solid 
  in 
  question, 
  (b) 
  

   many 
  of 
  the 
  parts 
  of 
  the 
  apparatus 
  and 
  the 
  adjustments 
  of 
  

   the 
  same 
  are 
  only 
  required 
  to 
  approximate 
  fairly 
  roughly 
  to 
  the 
  

   ideal 
  geometrical 
  conditions, 
  (c) 
  increased 
  accuracy 
  of 
  the 
  final 
  

   data, 
  (d) 
  simplicity 
  and 
  rigidity 
  of 
  the 
  apparatus, 
  and 
  (e) 
  

   nothing 
  more 
  elaborate 
  than 
  the 
  ordinary 
  equipment 
  of 
  any 
  

   physical 
  laboratory 
  is 
  necessary. 
  

  

  The 
  material 
  needed 
  comprises 
  a 
  goniometer 
  (or 
  spectro- 
  

   meter), 
  an 
  immersion 
  trough 
  having 
  glass 
  ends 
  parallel 
  to 
  each 
  

   other 
  (permissible 
  malconstruction 
  1°), 
  a 
  set 
  of 
  (5) 
  standard- 
  

   ized 
  glass 
  prisms 
  of 
  90° 
  refracting 
  angle, 
  a 
  set 
  of 
  liquids 
  pos- 
  

   sessing 
  a 
  fairly 
  wide 
  range 
  of 
  refractive 
  indices, 
  sources 
  of 
  light, 
  

   etc. 
  The 
  materials 
  of 
  the 
  prisms 
  used 
  by 
  Fabry 
  are 
  designated 
  

   as 
  : 
  light 
  boro-silicate 
  crown, 
  ordinary 
  crown, 
  light 
  barium 
  

   crown, 
  dense 
  flint, 
  and 
  very 
  dense 
  flint. 
  The 
  liquids 
  employed 
  

  

  