﻿OYSTERS 
  AND 
  METHODS 
  OF 
  OYSTER-CULTURE. 
  331 
  

  

  transverse 
  crossbars 
  h 
  b, 
  of 
  figs. 
  1, 
  2, 
  3, 
  and 
  4, 
  npon 
  which 
  the 
  permeable 
  tliaphragni 
  

   rests. 
  Fig. 
  1 
  represents 
  the 
  trunk 
  A 
  secured 
  within 
  a 
  pair 
  of 
  quadrangular 
  frames, 
  

   F 
  F, 
  and 
  partially 
  in 
  sectional 
  elevation 
  in 
  ]dace 
  in 
  the 
  trench 
  or 
  canal 
  leading 
  from 
  

   the 
  pond 
  to 
  the 
  open 
  water; 
  fig. 
  2 
  represents 
  the 
  construction 
  of 
  the 
  end 
  of 
  the 
  trunk 
  

   next 
  the 
  open 
  water, 
  and 
  fig. 
  3 
  that 
  of 
  the 
  end 
  next 
  the 
  pond, 
  while 
  fig. 
  4 
  shows 
  the 
  

   trunk 
  as 
  viewed 
  from 
  above. 
  

  

  On 
  the 
  crossbars 
  b 
  b 
  n 
  single 
  screen 
  of 
  galvanized 
  wire 
  cloth, 
  W, 
  fig. 
  1 
  (galvan- 
  

   ized 
  after 
  it 
  is 
  woven), 
  is 
  superimposed, 
  having 
  meshes, 
  say, 
  one-half 
  inch 
  in 
  diameter; 
  

   upon 
  the 
  wire 
  screen 
  a 
  layer 
  of 
  guuny-cloth, 
  C, 
  figs. 
  1 
  and 
  4, 
  is 
  laid, 
  upon 
  which 
  a 
  

   layer 
  of 
  fine, 
  clean 
  sand, 
  S, 
  is 
  spread 
  evenly 
  from 
  one 
  end 
  of 
  the 
  trunk 
  to 
  the 
  other. 
  

   The 
  end 
  board 
  e, 
  extemling 
  halfway 
  up 
  at 
  the 
  outer 
  end 
  of 
  tlie 
  box, 
  runs 
  tip 
  past 
  

   the 
  level 
  of 
  the 
  wire 
  and 
  cloth 
  to 
  confine 
  the 
  sand 
  at 
  that 
  extremity, 
  as 
  shown 
  in 
  

   fig. 
  2, 
  while 
  the 
  sand 
  is 
  confined 
  by 
  the 
  board 
  i 
  at 
  the 
  other 
  end 
  of 
  the 
  trunk 
  next 
  

   the 
  iioud, 
  as 
  shown 
  in 
  fig. 
  3. 
  The 
  wire 
  clotli 
  and 
  bars 
  b 
  b 
  constitute 
  the 
  support 
  

   for 
  the 
  sand 
  as 
  it 
  lies 
  upon 
  the 
  gunny-cloth, 
  which 
  is 
  supported 
  in 
  turn 
  by 
  the 
  wire 
  

   cloth 
  or 
  screen 
  TV. 
  This 
  is 
  essentially 
  the 
  construction 
  of 
  the 
  filtering 
  apparatus 
  in 
  

   which 
  the 
  layer 
  of 
  sand, 
  »S', 
  is 
  at 
  all 
  times 
  accessible, 
  so 
  that 
  it 
  can 
  be 
  removed 
  if 
  it 
  

   becomes 
  clogged 
  with 
  ooze 
  carried 
  in 
  by 
  successive 
  tides 
  under 
  the 
  gate 
  (i, 
  figs. 
  1, 
  

   2, 
  and 
  4. 
  This 
  layer 
  of 
  sand 
  can 
  also 
  be 
  increased 
  or 
  diminished 
  in 
  thickness 
  so 
  as 
  

   to 
  strain 
  the 
  inflowing 
  and 
  outflowing 
  water 
  more 
  or 
  less 
  effectually, 
  as 
  may 
  be 
  

   desired, 
  or 
  in 
  order 
  to 
  more 
  or 
  less 
  eff'ectually 
  prevent 
  the 
  escape 
  of 
  any 
  eggs 
  or 
  

   embryos 
  of 
  oyster 
  which 
  may 
  be 
  developing 
  within 
  the 
  pond 
  and 
  wafted 
  to 
  and 
  fro 
  

   by 
  the 
  eblting 
  and 
  flowing 
  currents 
  which 
  are 
  carried 
  in 
  and 
  out 
  of 
  the 
  pond 
  through 
  

   the 
  diaphragm 
  by 
  tidal 
  action. 
  The 
  gunny-cloth, 
  C, 
  fig. 
  4, 
  may 
  possibly 
  be 
  replaced 
  

   by, 
  first, 
  a 
  layer 
  of 
  coarse 
  gravel, 
  then 
  a 
  layer 
  of 
  finer 
  gravel 
  superimposed 
  upon 
  

   that, 
  which 
  would 
  prevent 
  the 
  fine 
  sand 
  from 
  sifting 
  through 
  the 
  supporting 
  wire 
  

   screen 
  W. 
  Gravel 
  would 
  be 
  more 
  durable 
  than 
  gunny-cloth 
  or 
  sacking, 
  which, 
  like 
  

   all 
  otiier 
  textile 
  fabrics, 
  will 
  rot 
  if 
  immersed 
  in 
  salt 
  water 
  for 
  a 
  few 
  weeks. 
  In 
  

   practice, 
  however, 
  a 
  mode 
  of 
  getting 
  overall 
  such 
  difliculties 
  would 
  soon 
  be 
  devised. 
  

   A 
  coarse 
  sacking 
  to 
  be 
  used 
  for 
  the 
  purpose 
  might 
  be 
  saturated 
  with 
  a 
  drying 
  oil 
  or 
  

   with 
  tar 
  diluted 
  with 
  oil 
  of 
  turpentine, 
  which 
  when 
  dry 
  would 
  act 
  as 
  a 
  preservative 
  

   of 
  the 
  material, 
  but 
  not 
  cause 
  it 
  to 
  become 
  impervious. 
  

  

  When 
  the 
  trunk 
  A 
  is 
  put 
  in 
  place 
  (which 
  should 
  be 
  done 
  before 
  the 
  water 
  is 
  let 
  

   into 
  a 
  freshly 
  excavated 
  pond, 
  and 
  also 
  before 
  the 
  water 
  is 
  let 
  into 
  the 
  trench 
  from 
  

   the 
  sea 
  end), 
  it 
  should 
  be 
  securely 
  placed 
  in 
  position 
  and 
  the 
  earth 
  tightly 
  rammed 
  

   in 
  along 
  the 
  sides 
  so 
  as 
  to 
  prevent 
  any 
  sea 
  water 
  from 
  finding 
  its 
  way 
  into 
  the 
  pond, 
  

   except 
  such 
  as 
  passes 
  through 
  the 
  filtering 
  diaphragm. 
  It 
  is 
  also 
  unnecessary 
  to 
  

   insist 
  that 
  the 
  trunk 
  be 
  constructed 
  in 
  such 
  a 
  way 
  that 
  it 
  will 
  be 
  practically 
  water- 
  

   tight, 
  and 
  not 
  liable 
  to 
  leak 
  between 
  the 
  planks 
  or 
  at 
  the 
  corners. 
  The 
  wire 
  cloth, 
  

   sacking, 
  or 
  gravel, 
  and 
  sand 
  having 
  been 
  got 
  into 
  place, 
  and 
  when 
  complete 
  forming 
  

   a 
  stratum 
  having 
  a 
  total 
  thickness 
  of 
  5 
  or 
  6 
  inches, 
  the 
  operator 
  is 
  ready 
  to 
  cut 
  

   away 
  the 
  barrier 
  at 
  the 
  sea 
  end 
  of 
  the 
  trench 
  and 
  let 
  in 
  the 
  water. 
  

  

  If 
  tlien 
  the 
  trunk 
  A 
  has 
  been 
  let 
  down 
  into 
  the 
  trench 
  deep 
  enough 
  the 
  sea 
  level 
  

   at 
  low 
  tide 
  ought 
  to 
  be 
  somewhat 
  above 
  the 
  upper 
  edge 
  of 
  the 
  board 
  e. 
  The 
  water 
  

   will 
  then, 
  as 
  the 
  tide 
  rises, 
  flow 
  back 
  over 
  the 
  sand 
  as 
  far 
  as 
  the 
  board 
  i, 
  and 
  will 
  per- 
  

   colate 
  through 
  the 
  diaphragm 
  into 
  the 
  space 
  /, 
  under 
  the 
  latter, 
  and 
  so 
  find 
  its 
  way 
  

   into 
  the 
  pond. 
  After 
  a 
  day 
  or 
  so 
  the 
  pond 
  will 
  be 
  filled 
  with 
  sea 
  water 
  which 
  has 
  

   practically 
  been 
  filtered, 
  and 
  filtered 
  more 
  or 
  less 
  eff'ectually 
  in 
  projiortion 
  to 
  the 
  

   thickness 
  of 
  the 
  stratum 
  of 
  sand 
  constituting 
  the 
  diaphragm. 
  After 
  the 
  pond 
  has 
  

   ouce 
  been 
  filled 
  with 
  the 
  rise 
  and 
  fall 
  of 
  the 
  tide 
  in 
  the 
  open 
  water 
  the 
  level 
  of 
  the 
  

   latter 
  and 
  that 
  in 
  the 
  pond 
  will 
  be 
  constantly 
  changing 
  ; 
  in 
  other 
  words, 
  when 
  the 
  tide 
  

   is 
  ebbing 
  the 
  water 
  level 
  in 
  the 
  pond 
  will 
  be 
  higher 
  than 
  that 
  of 
  the 
  water 
  outside, 
  

   as 
  in 
  fact 
  represented 
  at 
  wl 
  and 
  il 
  in 
  fig. 
  1. 
  Under 
  these 
  circumstances 
  there 
  will 
  

   be 
  a 
  supply 
  of 
  water 
  flowing 
  out 
  through 
  the 
  under 
  division 
  / 
  of 
  the 
  trunk 
  A, 
  up 
  

   through 
  the 
  sand 
  and 
  out 
  over 
  its 
  surface 
  through 
  the 
  outlet 
  O 
  under 
  the 
  gate 
  G. 
  

   After 
  the 
  ebb 
  tide 
  is 
  over 
  and 
  flood 
  tide 
  begins 
  these 
  levels 
  will 
  be 
  reversed 
  and 
  wl 
  

  

  