﻿330 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  In 
  the 
  beginning 
  of 
  his 
  first 
  paper 
  Bazin 
  remarks 
  that 
  the 
  the- 
  

   ory 
  of 
  the 
  weir 
  is 
  the 
  least 
  advanced 
  of 
  all 
  branches 
  of 
  hydraulics. 
  

   The 
  coefficients 
  used 
  in 
  practice 
  vary 
  between 
  such 
  wide 
  limits 
  

   that 
  in 
  most 
  cases 
  we 
  are 
  unable 
  to 
  make 
  a 
  rational 
  selection 
  

   from 
  the 
  many 
  numerical 
  values 
  assigned 
  to 
  them. 
  

  

  The 
  problem, 
  he 
  says, 
  is 
  in 
  fact 
  a 
  complicated 
  one, 
  being 
  con- 
  

   nected 
  on 
  the 
  one 
  hand 
  with 
  the 
  theory 
  of 
  flow 
  through 
  orifices 
  

   and 
  on 
  the 
  other 
  with 
  that 
  of 
  open 
  channels. 
  The 
  value 
  of 
  the 
  

   coefficients 
  in 
  each 
  case 
  is 
  influenced 
  by 
  many 
  elements. 
  Thus 
  

   we 
  ought 
  to 
  consider: 
  

  

  1) 
  The 
  velocity 
  of 
  approach; 
  that 
  is, 
  the 
  velocity 
  with 
  which 
  

   the 
  upstream 
  water 
  reaches 
  the 
  weir, 
  the 
  effect 
  of 
  which 
  can 
  not 
  

   be 
  neglected 
  in 
  weirs 
  of 
  small 
  hight.- 
  

  

  2) 
  The 
  contraction 
  of 
  the 
  vertical 
  section 
  of 
  the 
  stream 
  at 
  the 
  

   weir, 
  the 
  amount 
  depending 
  upon 
  the 
  hight 
  of 
  the 
  weir 
  and 
  the 
  

   form 
  of 
  the 
  crest. 
  

  

  3) 
  The 
  lateral 
  contraction 
  which, 
  though 
  unimportant 
  in 
  weirs 
  

   of 
  great 
  length, 
  seriously 
  modifies 
  the 
  results 
  in 
  shorter 
  weirs. 
  

  

  As 
  a 
  further 
  condition, 
  Bazin 
  points 
  out 
  that 
  when 
  the 
  down- 
  

   stream 
  channel 
  has 
  a 
  width 
  of 
  the 
  length 
  of 
  the 
  weir, 
  so 
  that 
  the 
  

   overflowing 
  sheet 
  of 
  water, 
  or 
  nappe, 
  touches 
  at 
  the 
  sides, 
  thus 
  

   preventing 
  free 
  admission 
  of 
  air 
  under 
  the 
  nappe, 
  there 
  occur 
  

   special 
  phenomena 
  greatly 
  affecting 
  the 
  flow. 
  1 
  

  

  Bazin's 
  method 
  of 
  experimentation 
  may 
  be 
  referred 
  to 
  briefly. 
  

   A 
  standard 
  weir 
  was 
  set 
  up 
  at 
  the 
  head 
  of 
  a 
  long 
  chamber, 
  in 
  

   which 
  the 
  actual 
  volume 
  passing 
  over 
  was 
  measured 
  a 
  sufficient 
  

   number 
  of 
  times 
  to 
  give 
  averages, 
  which 
  Bazin 
  considers 
  are 
  

   accurate 
  to 
  within 
  probably 
  less 
  than 
  1 
  per 
  cent. 
  Having 
  estab- 
  

   lished 
  in 
  this 
  way 
  the 
  values 
  of 
  the 
  coefficients 
  for 
  a 
  standard 
  

   weir, 
  with 
  heads 
  varying 
  from 
  about 
  0.164 
  ft. 
  to 
  1.969 
  ft., 
  the 
  

   experiments 
  on 
  weirs 
  of 
  irregular 
  profiles 
  were 
  made 
  by 
  placing 
  

  

  i 
  Bazin's 
  earlier 
  papers 
  are 
  directed 
  specially 
  to 
  a 
  detailed 
  investigation 
  

   of 
  these 
  several 
  points. 
  Space 
  will 
  not 
  be 
  taken 
  here 
  to 
  describe 
  his 
  experi- 
  

   ments 
  in 
  detail. 
  The 
  original 
  data 
  may 
  be 
  found 
  in 
  the 
  Annates 
  des 
  Ponts 
  ct 
  

   CJiaussces 
  for 
  the 
  years 
  already 
  cited. 
  A 
  translation 
  of 
  the 
  earlier 
  num- 
  

   bers 
  has 
  also 
  been 
  made 
  by 
  Messrs. 
  Arthur 
  Marichal 
  and 
  John 
  C. 
  Traut- 
  

   wine 
  Jr., 
  and 
  may 
  be 
  found 
  in 
  the 
  Proceedings 
  of 
  the 
  Engineers' 
  Club 
  of 
  

   Philadelphia 
  for 
  January, 
  1890 
  ; 
  July, 
  1892 
  ; 
  October, 
  1892, 
  and 
  April, 
  1893. 
  

  

  