﻿252 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  

  

  ing 
  the 
  specific 
  gravity 
  of 
  ordinary 
  sea 
  water, 
  and 
  No. 
  2 
  for 
  water 
  

   between 
  these 
  grades. 
  

  

  The 
  specific 
  gravity 
  varies 
  to 
  some 
  extent 
  with 
  the 
  temperature, 
  

   being 
  less 
  when 
  the 
  water 
  is 
  warm 
  than 
  when 
  cold. 
  Thus 
  in 
  work 
  

   requiring 
  very 
  great 
  accuracy 
  it 
  is 
  necessary 
  to 
  standardize 
  all 
  

   specific 
  gravity 
  observations 
  — 
  that 
  is, 
  to 
  calculate 
  the 
  error 
  in 
  each 
  

   case 
  due 
  to 
  temperature 
  with 
  reference 
  to 
  an 
  adopted 
  standard. 
  For 
  

   all 
  practical 
  purposes, 
  however, 
  this 
  inaccuracy 
  is 
  not 
  great 
  enough 
  to 
  

   materially 
  modify 
  results, 
  and 
  may 
  be 
  disregarded. 
  

  

  The 
  water 
  over 
  the 
  oyster 
  beds 
  was 
  examined 
  frequently 
  at 
  different 
  

   stages 
  of 
  the 
  tide 
  and 
  at 
  different 
  seasons 
  of 
  the 
  year. 
  Readings 
  from 
  

   the 
  salinometers 
  were 
  regularly 
  taken 
  and 
  recorded, 
  and 
  at 
  the 
  end 
  of 
  

   each 
  month 
  a 
  general 
  average 
  was 
  made. 
  These 
  averages 
  appear 
  in 
  

   this 
  report 
  in 
  the 
  food 
  tables. 
  

  

  The 
  apparatus 
  for 
  determining 
  the 
  velocity 
  and 
  direction 
  of 
  the 
  

   currents 
  which 
  flow 
  over 
  the 
  oyster 
  ])eds 
  was 
  designed 
  by 
  Prof. 
  J. 
  A. 
  

   Holmes 
  and 
  consists 
  of 
  a 
  cylindrical 
  "drag" 
  suspended 
  by 
  a 
  wire 
  

   from 
  a 
  small 
  floating 
  buoy. 
  The 
  distance 
  between 
  the 
  buoy 
  and 
  the 
  

   drag 
  is 
  regulated 
  according 
  to 
  the 
  depth 
  of 
  the 
  water, 
  the 
  aim 
  being 
  to 
  

   have 
  the 
  drag 
  suspended 
  in 
  the 
  swiftest 
  part 
  of 
  the 
  current. 
  To 
  the 
  

   buoy 
  or 
  float 
  is 
  attached 
  a 
  long 
  line, 
  wound 
  upon 
  a 
  reel, 
  on 
  which 
  are 
  

   tied 
  at 
  intervals 
  of 
  50 
  feet 
  small 
  pieces 
  of 
  colored 
  cloth. 
  In 
  determin- 
  

   ing 
  the 
  velocity 
  of 
  the 
  current 
  in 
  a 
  certain 
  locality 
  by 
  means 
  of 
  this 
  

   apparatus, 
  a 
  launch 
  or 
  other 
  boat 
  was 
  first 
  anchored 
  in 
  the 
  channel 
  and 
  

   the 
  drag 
  and 
  float 
  lowered 
  from 
  the 
  stern. 
  As 
  soon 
  as 
  the 
  drag 
  filled 
  

   with 
  water 
  and 
  sank, 
  the 
  line 
  was 
  allowed 
  to 
  pay 
  out 
  until 
  the 
  first 
  

   mark 
  appeared; 
  it 
  was 
  then 
  held 
  until 
  the 
  timekeeper 
  gave 
  the 
  signal 
  

   to 
  set 
  it 
  free. 
  The 
  time 
  required 
  for 
  each 
  of 
  the 
  marks 
  on 
  the 
  line 
  to 
  

   be 
  carried 
  past 
  a 
  mark 
  on 
  the 
  stern 
  of 
  the 
  boat 
  was 
  noted, 
  and 
  from 
  

   these 
  observed 
  intervals 
  the 
  rate 
  of 
  the 
  current 
  per 
  mile 
  was 
  calculated. 
  

   Numerous 
  observations 
  and 
  calculations 
  of 
  this 
  kind 
  were 
  made 
  in 
  

   each 
  locality, 
  and 
  an 
  average 
  was 
  computed. 
  These 
  are 
  shown 
  on 
  the 
  

   charts 
  and 
  in 
  the 
  text. 
  

  

  The 
  character 
  of 
  the 
  l^ottom 
  in 
  each 
  locality 
  was 
  carefully 
  examined, 
  

   first 
  by 
  means 
  of 
  a 
  sounding 
  rod, 
  and 
  then 
  from 
  a 
  sample 
  collected 
  ))y 
  

   using 
  a 
  short 
  piece 
  of 
  sharpened 
  iron 
  piping 
  welded 
  to 
  a 
  long 
  iron 
  rod. 
  

   This 
  being 
  thrust 
  into 
  the 
  bottom, 
  unless 
  the 
  latter 
  were 
  composed 
  of 
  

   pure 
  sand 
  or 
  shells, 
  the 
  instrument 
  came 
  up 
  filled. 
  The 
  contents 
  were 
  

   examined 
  in 
  the 
  laboratory 
  under 
  the 
  microscope 
  when 
  desirable. 
  

  

  The 
  constituents 
  of 
  the 
  food 
  of 
  oj^sters 
  have 
  been 
  repeatedly 
  deter- 
  

   mined, 
  but 
  the 
  cases 
  are 
  few 
  in 
  which 
  attempts 
  have 
  been 
  made 
  to 
  

   ascertain 
  the 
  amount 
  of 
  each 
  constituent 
  and 
  its 
  source. 
  The 
  inter- 
  

   esting 
  qualitative 
  examinations 
  made 
  by 
  Lotsy 
  '^ 
  gave 
  a 
  general 
  idea 
  of 
  

  

  a 
  J. 
  P. 
  Lotsy.— 
  The 
  Food 
  of 
  the 
  Oyster, 
  Clam, 
  and 
  Ribbed 
  Mussel. 
  U. 
  S. 
  F. 
  C. 
  Report 
  1893, 
  pp. 
  376-386. 
  

  

  