﻿194 
  KEPOET 
  OF 
  COMMISSIONEE 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [10J 
  

  

  during 
  its 
  descent 
  through 
  the 
  water, 
  the 
  time 
  figures 
  deduced 
  from 
  

   laboratory 
  observations 
  may 
  be 
  too 
  large 
  ; 
  but 
  it 
  seems 
  hardly 
  safe 
  to 
  

   rely 
  upon 
  seven 
  minutes' 
  exposure, 
  as 
  directed 
  by 
  Sigsbee, 
  in 
  the 
  opera- 
  

   tions 
  of 
  the 
  Blake 
  (op. 
  cit., 
  p. 
  23), 
  and 
  still 
  less 
  upon 
  five 
  minutes' 
  ex- 
  

   posure, 
  as 
  was 
  directed 
  and 
  followed 
  in 
  the 
  Challenger 
  work.* 
  

  

  Unless 
  the 
  thermometers 
  are 
  always 
  kept 
  bulb 
  uppermost 
  (for 
  which 
  

   reason 
  the 
  makers 
  ship 
  them 
  in 
  cases 
  of 
  a 
  pyramidal 
  formXthe 
  mercury 
  

   is 
  very 
  likely 
  to 
  get 
  above 
  the 
  indices. 
  In 
  such 
  an 
  event 
  the 
  index 
  may 
  

   be 
  drawn 
  by 
  the 
  magnet 
  into 
  the 
  small 
  enlargement 
  just 
  below 
  the 
  bulb, 
  

   when 
  the 
  mercury 
  will 
  free 
  itself 
  and 
  drop 
  back 
  into 
  the 
  tubes 
  ; 
  but 
  it 
  

   will 
  not 
  always 
  be 
  easy 
  to 
  get 
  the 
  index 
  back 
  into 
  the 
  tube 
  again, 
  as 
  it 
  

   is 
  likely 
  to 
  tip 
  under 
  the 
  influence 
  of 
  the 
  magnet, 
  and 
  to 
  catch 
  against 
  

   the 
  sides 
  of 
  the 
  small 
  enlargement. 
  In 
  the 
  course 
  of 
  the 
  tapping 
  upon 
  

   a 
  table 
  and 
  swinging 
  the 
  thermometer 
  about 
  the 
  bead, 
  which 
  are 
  to 
  be 
  

   tried 
  in 
  case 
  of 
  such 
  an 
  accident, 
  it 
  is 
  very 
  likely 
  that 
  the 
  tube 
  will 
  be 
  

   started 
  a 
  little 
  from 
  its 
  right 
  place 
  upon 
  the 
  scale, 
  since 
  the 
  fastening 
  

   which 
  is 
  intended 
  to 
  secure 
  the 
  tube 
  at 
  the 
  bend 
  of 
  the 
  U 
  is 
  a 
  soft 
  cop- 
  

   per 
  band, 
  fastened 
  by 
  one 
  end 
  only, 
  probably 
  to 
  allow 
  for 
  expansion 
  or 
  

   contraction 
  of 
  the 
  glass, 
  under 
  wide 
  variations 
  of 
  temperature 
  or 
  

   pressure. 
  

  

  As 
  to 
  breaks 
  in 
  the 
  mercurial 
  column, 
  an 
  accident 
  common 
  to 
  all 
  

   mercurial 
  thermometers, 
  and 
  other 
  small 
  mischances 
  which 
  may 
  be 
  

   remedied 
  by 
  the 
  observer 
  himself, 
  I 
  cannot 
  do 
  better 
  than 
  refer 
  to 
  Sigs- 
  

   bee's 
  monograph, 
  already 
  often 
  quoted 
  (p. 
  110), 
  for 
  clear 
  and 
  practical 
  

   directions 
  as 
  to 
  all 
  that 
  may 
  be 
  safely 
  done 
  without 
  sending 
  the 
  instru- 
  

   ments 
  back 
  to 
  the 
  maker 
  for 
  repair. 
  

  

  Pressure 
  errors. 
  — 
  In 
  the 
  Challenger 
  observations 
  a 
  subtractive 
  correc- 
  

   tion 
  of 
  about 
  i° 
  F., 
  applied 
  to 
  the 
  maximum 
  side, 
  was 
  assigned 
  by 
  Dr. 
  

   Wyville 
  Thomson 
  for 
  every 
  mile 
  of 
  depth 
  below 
  the 
  surface 
  of 
  the 
  sea. 
  

   This 
  correction 
  was 
  the 
  result 
  of 
  a 
  series 
  of 
  careful 
  observations 
  made, 
  

   with 
  the 
  aid 
  of 
  a 
  powerful 
  hydraulic 
  press, 
  by 
  Capt. 
  J. 
  E. 
  Davis, 
  R. 
  N.,t 
  

   assisted 
  by 
  Prof. 
  W. 
  Allen 
  Miller 
  and 
  others. 
  Since 
  the 
  return 
  of 
  the 
  

   Challenger, 
  and 
  during 
  the 
  three 
  years 
  preceding 
  July, 
  1881, 
  the 
  press- 
  

   ure-error 
  of 
  these 
  thermometers 
  has 
  been 
  made 
  the 
  subject 
  of 
  especial 
  

   examination 
  by 
  Prof. 
  P. 
  G. 
  Tait, 
  whose 
  conclusions 
  are 
  published 
  as 
  

   Appendix 
  A 
  of 
  the 
  second 
  volume 
  of 
  the 
  narrative 
  part 
  of 
  the 
  " 
  General 
  

   Eeport 
  on 
  the 
  scientific 
  results 
  of 
  the 
  voyage 
  of 
  H. 
  M. 
  S. 
  Challenger," 
  

   already 
  cited. 
  In 
  the 
  experiments 
  of 
  both 
  Captain 
  Davis 
  and 
  Professor 
  

   Tait, 
  the 
  thermometers 
  were 
  subjected 
  to 
  heavy 
  pressures 
  in 
  a 
  hydraulic 
  

   press, 
  and 
  the 
  phenomena 
  presented 
  were 
  similar 
  in 
  both 
  series. 
  Pro- 
  

   fessor 
  Tait 
  concludes, 
  however, 
  that 
  Captain 
  Davis's 
  corrections 
  (and 
  

   consequently 
  those 
  of 
  the 
  Challenger 
  report) 
  are 
  too 
  large, 
  for 
  the 
  follow- 
  

   ing 
  reasons 
  : 
  In 
  the 
  first 
  place 
  the 
  water 
  in 
  the 
  press 
  is 
  heated 
  by 
  com- 
  

  

  * 
  Challenger 
  Narrative, 
  vol. 
  1, 
  p. 
  120. 
  

  

  t 
  See 
  his 
  paper 
  on 
  "Deep-sea 
  thermometers" 
  in 
  Proceedings 
  of 
  Meteorological 
  

   Society, 
  April, 
  1871. 
  

  

  