﻿HOW 
  DEEP 
  IS 
  THE 
  OCEAN? 
  — 
  ABBOT. 
  281 
  

  

  splashing 
  of 
  waves. 
  Sounds 
  of 
  extremely 
  high 
  pitch 
  are 
  therefore 
  

   better 
  for 
  signalling 
  purposes. 
  Not 
  only 
  can 
  such 
  signals 
  be 
  heard 
  

   directly 
  but 
  the 
  echoes 
  of 
  them 
  from 
  the 
  bottom 
  of 
  the 
  ocean 
  can 
  

   be 
  heard 
  too. 
  Therefore 
  it 
  is 
  easy 
  to 
  see 
  in 
  principle 
  how 
  by 
  measur- 
  

   ing 
  the 
  angle 
  from 
  which 
  the 
  echo 
  sounds 
  come 
  up 
  to 
  the 
  receivers 
  

   one 
  could 
  determine 
  the 
  distance 
  to 
  the 
  bottom. 
  For 
  with 
  sound 
  

   as 
  with 
  a 
  billiard 
  ball 
  (played 
  without 
  English) 
  the 
  angles 
  of 
  the 
  

   path 
  at 
  the 
  reflecting 
  surface 
  are 
  equal. 
  Knowing 
  the 
  ship's 
  length 
  

   and 
  the 
  angle 
  the 
  sound 
  appears 
  to 
  come 
  from, 
  it 
  is 
  therefore 
  easy 
  

   to 
  calculate 
  the 
  depth. 
  But 
  this 
  scheme 
  is 
  good 
  only 
  for 
  depths 
  less 
  

   than 
  two 
  or 
  three 
  times 
  the 
  ship's 
  length. 
  Beyond 
  that 
  the 
  errors 
  

   of 
  measuring 
  the 
  angles 
  produce 
  too 
  much 
  error 
  in 
  the 
  result. 
  

  

  Doctor 
  Hayes 
  has 
  worked 
  out 
  another 
  scheme 
  for 
  greater 
  depths. 
  

   This 
  depends 
  on 
  measuring 
  the 
  time 
  between 
  sending 
  the 
  signal 
  

   and 
  receiving 
  its 
  echo. 
  Sound 
  travels 
  800 
  fathoms 
  per 
  second 
  in 
  

   water. 
  Hence 
  it 
  can 
  easily 
  be 
  seen 
  that 
  a 
  stop 
  watch 
  would 
  not 
  be 
  

   accurate 
  enough, 
  for 
  an 
  error 
  of 
  one-fifth 
  of 
  a 
  second 
  would 
  mean 
  

   the 
  half 
  of 
  160 
  or 
  80 
  fathoms 
  in 
  depth. 
  An 
  indirect 
  process 
  is 
  

   used. 
  Sounds 
  are 
  sent 
  out 
  at 
  equal 
  intervals. 
  A 
  very 
  accurate 
  and 
  

   controllable 
  mechanism 
  is 
  used 
  so 
  that 
  not 
  only 
  are 
  the 
  intervals 
  

   between 
  the 
  signals 
  exactly 
  equal 
  but 
  the 
  interval 
  can 
  be 
  varied 
  in 
  

   length 
  between 
  wide 
  limits. 
  It 
  will 
  be 
  seen 
  that 
  as 
  the 
  interval 
  is 
  

   changed 
  it 
  can 
  be 
  arranged 
  so 
  that 
  one 
  ear 
  will 
  hear 
  the 
  series 
  of 
  

   sounds 
  directly 
  at 
  the 
  same 
  instant 
  that 
  the 
  other 
  ear 
  hears 
  them 
  

   through 
  the 
  hydrophone 
  as 
  an 
  echo 
  from 
  the 
  bottom. 
  

  

  If 
  the 
  time 
  intervals 
  are 
  read 
  off 
  from 
  the 
  scale 
  of 
  the 
  sending 
  

   machine, 
  and 
  if 
  one 
  could 
  be 
  sure 
  that 
  the 
  coincidence 
  was 
  caused 
  

   by 
  the 
  interval 
  being 
  just 
  long 
  enough 
  for 
  the 
  sound 
  to 
  go 
  to 
  the 
  bot- 
  

   tom 
  and 
  back, 
  that 
  would 
  be 
  enough. 
  But 
  it 
  is 
  plain 
  that, 
  by 
  speed- 
  

   ing 
  up, 
  the 
  interval 
  could 
  be 
  shortened 
  so 
  much 
  that 
  there 
  would 
  

   again 
  be 
  a 
  coincidence. 
  Again 
  it 
  could 
  be 
  shortened 
  still 
  more 
  till 
  

   a 
  third 
  coincidence 
  came, 
  and 
  so 
  on. 
  But 
  it 
  is 
  clear 
  that 
  the 
  lengths 
  

   of 
  these 
  several 
  intervals 
  that 
  gave 
  coincidences 
  would 
  be 
  as 
  1 
  to 
  

   1/2 
  to 
  1/3, 
  and 
  so 
  on. 
  From 
  this 
  it 
  is 
  easy 
  to 
  tell 
  just 
  which 
  coinci- 
  

   dence 
  we 
  are 
  using. 
  

  

  This 
  method 
  of 
  measuring 
  depths 
  has 
  been 
  made 
  exceedingly 
  

   accurate 
  for 
  all 
  distances 
  above 
  40 
  fathoms, 
  and 
  so 
  it 
  joins 
  onto 
  the 
  

   other 
  one 
  to 
  cover 
  all 
  ocean 
  depths. 
  The 
  first 
  big 
  test 
  of 
  it 
  on 
  an 
  

   actual 
  cruise 
  was 
  made 
  in 
  June, 
  1922, 
  on 
  a 
  run 
  of 
  the 
  U. 
  S. 
  destroyer 
  

   Stewart 
  from 
  Newport, 
  R. 
  I., 
  to 
  the 
  Straits 
  of 
  Gibraltar. 
  This 
  voy- 
  

   age 
  was 
  made 
  in 
  nine 
  days. 
  During 
  it 
  and 
  while 
  proceeding 
  at 
  usual 
  

   speed, 
  several 
  hundred 
  soundings 
  were 
  made 
  as 
  shown 
  on 
  figure 
  4. 
  

   The 
  depths 
  observed 
  ranged 
  from 
  less 
  than 
  100 
  fathoms 
  during 
  the 
  

  

  