﻿T. 
  A 
  . 
  Jaggar, 
  Jr. 
  — 
  Simple 
  Instrument 
  for 
  inclining, 
  etc. 
  129 
  

  

  Art. 
  XII. 
  — 
  A 
  Simple 
  Instrument 
  for 
  inclining 
  a 
  Prepara- 
  

   tion 
  in 
  the 
  Microscope 
  ; 
  by 
  T. 
  A. 
  Jaggar, 
  Jr. 
  

  

  The 
  instrument* 
  here 
  described 
  was 
  devised 
  for 
  use 
  in 
  

   petrography, 
  especially 
  in 
  connection 
  with 
  the 
  Michel-Levyf 
  

   and 
  von 
  Fedorow;); 
  optical 
  methods 
  of 
  determining 
  feldspars. 
  

   The 
  device 
  may 
  be 
  of 
  service 
  to 
  microscopists 
  in 
  other 
  fields 
  

   as 
  well, 
  where 
  it 
  is 
  frequently 
  necessary 
  to 
  examine 
  in 
  reflected 
  

   light 
  the 
  surface 
  of 
  objects, 
  whose 
  relief 
  above 
  the 
  object- 
  

   glass 
  makes 
  tipping 
  imperative 
  if 
  one 
  desires 
  to 
  view 
  the 
  pre- 
  

   paration 
  on 
  all 
  sides. 
  

  

  In 
  the 
  study 
  of 
  thin 
  sections 
  of 
  rock 
  in 
  the 
  polarizing 
  

   microscope, 
  the 
  constituent 
  minerals 
  are 
  sliced 
  on 
  planes 
  bear- 
  

   ing 
  usually 
  no 
  definite 
  relation 
  to 
  the 
  optical 
  symmetry 
  of 
  the 
  

   individual 
  crystals 
  ; 
  in 
  order 
  to 
  obtain 
  sections 
  parallel 
  or 
  per- 
  

   pendicular 
  to 
  directions 
  of 
  optical 
  constancy 
  in 
  particular 
  min- 
  

   erals 
  of 
  such 
  a 
  rock 
  section, 
  it 
  has 
  been 
  necessary, 
  in 
  the 
  past, 
  

   to 
  seek 
  out 
  individuals 
  whose 
  orientation 
  chanced 
  to 
  give 
  the 
  

   results 
  desired, 
  or 
  to 
  average 
  a 
  number 
  of 
  approximately 
  

   accurate 
  sections, 
  or 
  to 
  isolate 
  the 
  mineral 
  and 
  grind 
  special 
  

   sections 
  oriented 
  with 
  reference 
  to 
  known 
  cleavages 
  or 
  crystal 
  

   faces. 
  By 
  using 
  the 
  so-called 
  " 
  Universal 
  Stage," 
  which 
  per- 
  

   mits 
  rotation 
  of 
  the 
  object-glass 
  about 
  two 
  axes 
  at 
  right 
  angles 
  

   to 
  each 
  other, 
  von 
  Fedorow 
  has 
  shown 
  that 
  a 
  crystal 
  section 
  

   may 
  be 
  oriented 
  at 
  will 
  with 
  reference 
  to 
  the 
  polarization 
  plane 
  

   of 
  the 
  nicols, 
  by 
  simply 
  inclining 
  it, 
  first 
  in 
  one 
  direction, 
  then 
  

   in 
  a 
  second 
  at 
  right 
  angles 
  to 
  the 
  first, 
  until 
  at 
  length 
  the 
  

   desired 
  optical 
  effect 
  is 
  observed. 
  

  

  For 
  certain 
  measurements 
  of 
  extreme 
  precision 
  in 
  micro- 
  

   scopical 
  crystallography, 
  the 
  graduated 
  circles 
  of 
  the 
  universal 
  

   stage 
  are 
  indispensable 
  : 
  but 
  for 
  the 
  determination 
  of 
  the 
  feld- 
  

   spars 
  by 
  symmetrical 
  extinctions, 
  or 
  for 
  conoscopic 
  work, 
  in 
  

   petrography, 
  all 
  that 
  is 
  required 
  in 
  practice 
  is 
  the 
  means 
  of 
  

   tipping 
  the 
  slide 
  with 
  delicacy 
  in 
  any 
  azimuth 
  at 
  will. 
  An 
  

   instrument 
  for 
  this 
  purpose 
  should 
  be 
  simple, 
  inexpensive, 
  

   easily 
  manipulated, 
  adaptable 
  to 
  any 
  microscope 
  and 
  instantly 
  

   removable 
  ; 
  to 
  meet 
  these 
  requirements 
  the 
  instrument 
  here 
  

   described 
  has 
  been 
  constructed. 
  

  

  The 
  accompanying 
  figure 
  (fig. 
  1) 
  shows 
  the 
  construction 
  of 
  the 
  

   instrument 
  in 
  vertical 
  section 
  and 
  plan, 
  natural 
  scale. 
  It 
  is 
  

  

  * 
  The 
  author's 
  model 
  was 
  made 
  by 
  C. 
  Milton 
  Chase, 
  mechanician, 
  45 
  Cam- 
  

   bridge 
  st., 
  Boston, 
  Mass. 
  The 
  Bausch 
  and 
  Lomb 
  Optical 
  Co., 
  of 
  Rochester, 
  N. 
  Y., 
  

   have 
  completed 
  a 
  new 
  model, 
  adaptable 
  to 
  the 
  stage 
  of 
  any 
  microscope, 
  when 
  

   size 
  and 
  distance 
  apart 
  of 
  clip-holes 
  are 
  specified. 
  

  

  f 
  A 
  Michel-Levy: 
  Etude 
  sur 
  la 
  determination 
  des 
  feldspaths 
  dans 
  les 
  plaques 
  

   minces, 
  au 
  point 
  de 
  vue 
  de 
  la 
  classification 
  des 
  roches. 
  Paris, 
  1894. 
  

  

  % 
  E. 
  von 
  Fedorow: 
  Universal-(Theodolith-) 
  Method 
  in 
  der 
  Mineralogie 
  und 
  

   Petrographie. 
  II. 
  Theil: 
  Krystall-optische 
  Untersuchungen, 
  Zeitschrift 
  fur 
  

   Krystallographie, 
  etc., 
  xxii, 
  229-268, 
  1893. 
  

  

  