﻿260 
  PROCEEDINGS 
  OP 
  THE 
  CALIFORNIA 
  

  

  ungen 
  der 
  Deiitschen 
  Gesellschaft 
  fiir 
  Natur 
  und 
  Volkerkunde 
  Ostasiens, 
  Stes, 
  

   Heft, 
  Yokohama, 
  Sept., 
  1873. 
  Proceedings 
  American 
  Academy 
  of 
  Arts 
  and 
  

   Sciences, 
  Vol. 
  VIII, 
  May, 
  1868-73. 
  The 
  Engineering 
  and 
  Mining 
  Journal, 
  

   Vol. 
  XVII, 
  Nos. 
  5 
  and 
  6. 
  Nature, 
  Vol. 
  IX, 
  Nos. 
  220, 
  221. 
  

  

  Donations 
  to 
  the 
  Museum 
  : 
  From 
  W. 
  H. 
  Ball, 
  large 
  collection 
  

   of 
  Fossils 
  of 
  the 
  post-pliocene 
  period, 
  from 
  Esmeralda, 
  Equador, 
  

   collected 
  by 
  Captain 
  A. 
  R. 
  Hodgkins, 
  of 
  the 
  schooner 
  " 
  Urania 
  "; 
  

   from 
  Prof. 
  Davidson, 
  a 
  crustacean 
  from 
  the 
  Island 
  of 
  San 
  Miguel 
  ; 
  

   from 
  Captain 
  E. 
  E. 
  Smith, 
  specimens 
  of 
  Coal 
  from 
  the 
  Arctic 
  coast, 
  

   near 
  Cape 
  Lisburne. 
  The 
  coal 
  was 
  observed 
  in 
  that 
  locality 
  for 
  a 
  

   distance 
  of 
  thirty 
  to 
  forty 
  miles, 
  and 
  crops 
  out 
  in 
  veins 
  of 
  great 
  

   thickness 
  ; 
  from 
  Mrs. 
  James 
  McEwen, 
  an 
  object 
  supposed 
  to 
  be 
  a 
  

   petrifaction, 
  obtained 
  on 
  the 
  Peso 
  Caliente 
  Rancho, 
  Sonoma 
  county, 
  

   in 
  a 
  portion 
  known 
  as 
  the 
  Indian 
  Garden. 
  

  

  The 
  following 
  paper 
  was 
  read 
  by 
  the 
  President 
  : 
  

  

  On 
  Improvements 
  in 
  the 
  Sextant. 
  

  

  BY 
  GEORGE 
  DAVIDSON. 
  

  

  The 
  sextant 
  is 
  the 
  most 
  universal 
  of 
  instruments 
  in 
  the 
  hands 
  of 
  the 
  geog- 
  

   rapher, 
  navigator 
  and 
  astronomer, 
  because 
  it 
  alone 
  is 
  available 
  at 
  sea 
  as 
  well 
  

   as 
  on 
  land. 
  To 
  the 
  navigator 
  it 
  is 
  invaluable; 
  and 
  in 
  the 
  special 
  work 
  of 
  

   hydrography 
  along 
  a 
  coast 
  line, 
  where 
  the 
  position 
  of 
  the 
  boat 
  or 
  vessel 
  is 
  gen- 
  

   erally 
  determined 
  by 
  observing 
  from 
  the 
  boat, 
  the 
  sextant 
  is 
  the 
  only 
  instrument 
  

   of 
  precision 
  in 
  use 
  ; 
  and 
  yet 
  in 
  its 
  present 
  forms, 
  it 
  has 
  certain 
  deficiencies 
  

   which 
  prevent 
  its 
  universality 
  of 
  application. 
  It 
  fails 
  to 
  measure 
  the 
  angles 
  

   between 
  one 
  hundred 
  and 
  forty 
  and 
  one 
  hundred 
  and 
  eighty 
  degrees 
  ; 
  and 
  the 
  

   hydrographers 
  of 
  all 
  countries 
  have 
  studied 
  to 
  remedy 
  this 
  defect 
  with 
  only 
  par- 
  

  

  • 
  -tiBl 
  success. 
  

  

  ■M. 
  Daussy, 
  the 
  French 
  hydrographer, 
  measurably 
  solved 
  the 
  problem 
  by 
  a 
  

   device 
  as 
  simple 
  iu 
  construction 
  and 
  beautiful 
  in 
  theory 
  as 
  it 
  is 
  difiBcult 
  in 
  

   practice. 
  By 
  means 
  of 
  a 
  second 
  horizon 
  glass, 
  he 
  added, 
  as 
  it 
  were, 
  a 
  constant 
  

  

  -angle 
  of 
  about 
  ninety 
  degrees 
  to 
  that 
  measured 
  by 
  the 
  index 
  and 
  horizon 
  

   glasses, 
  and 
  thus 
  obtained 
  any 
  angle 
  from 
  naught 
  to 
  one 
  hundred 
  and 
  eighty 
  de- 
  

   grees. 
  , 
  In 
  observing 
  large 
  angles 
  he 
  reflects 
  both 
  objects, 
  which 
  increases 
  the 
  

   difficulty 
  of 
  manipulation 
  by 
  the 
  observer 
  even 
  when 
  on 
  land, 
  with 
  well 
  defined 
  

   objects 
  ; 
  but 
  when 
  the 
  observer 
  is 
  in 
  a 
  boat, 
  disturbed 
  by 
  the 
  waves, 
  and 
  both 
  

   objects 
  indistinct, 
  it 
  is 
  next 
  to 
  impossible 
  to 
  see 
  them 
  ; 
  and 
  certainly 
  not 
  with 
  

  

  .any 
  degree 
  of 
  quickness, 
  which 
  such 
  operations 
  especially 
  demand. 
  Daussy's 
  

   instrument 
  has 
  not, 
  come 
  into 
  practical 
  use. 
  

  

  Pistor 
  .& 
  Martins, 
  of 
  Berlin, 
  have 
  also 
  partially 
  solved 
  the 
  same 
  problem 
  

   with, 
  the 
  prisBUitic 
  sextant 
  bearing 
  their 
  name. 
  This 
  instrument 
  will 
  measure 
  

  

  