﻿42 
  Transactions. 
  — 
  Miscellaneous. 
  

  

  In 
  estimating 
  the 
  quantity 
  of 
  sewage 
  to 
  be 
  carried 
  off 
  " 
  provision 
  lias 
  

   been 
  made 
  for 
  an 
  increase 
  of 
  the 
  ijopulation 
  up 
  to 
  30,000 
  people 
  to 
  the 
  

   square 
  mile, 
  except 
  over 
  the 
  outlying 
  districts, 
  where 
  provision 
  has 
  been 
  

   made 
  for 
  a 
  population 
  giving 
  20,000 
  to 
  the 
  square 
  mile." 
  "An 
  improved 
  

   water 
  supply, 
  equal 
  to 
  five 
  cubic 
  feet, 
  or 
  31:^ 
  gallons 
  per 
  head 
  for 
  such 
  

   contemplated 
  increased 
  poj^ulation 
  has 
  moreover 
  been 
  anticipated." 
  

  

  Again 
  : 
  " 
  How 
  to 
  dispose 
  of 
  the 
  rainfall 
  is 
  a 
  question 
  of 
  considerable 
  

   difficulty, 
  and 
  has 
  given 
  rise 
  to 
  much 
  diversity 
  of 
  opinion. 
  This 
  arises 
  

   from 
  the 
  fact 
  that, 
  whilst 
  it 
  is 
  in 
  itself 
  harmless, 
  and 
  even 
  advantageous 
  to 
  

   the 
  river, 
  it 
  sometimes 
  falls 
  suddenly 
  in 
  large 
  quantities. 
  These 
  considera- 
  

   tions 
  have 
  induced 
  theorists 
  to 
  advocate 
  that 
  the 
  rainfall 
  should 
  not 
  be 
  

   allowed 
  to 
  flow 
  off 
  with 
  tlie 
  sewage, 
  but 
  should 
  be 
  dealt 
  with 
  by 
  a 
  separate 
  

   system 
  of 
  sewers. 
  This 
  theory 
  however 
  is 
  most 
  impracticable." 
  

  

  Eeferring 
  to 
  experiments 
  on 
  this 
  subject 
  the 
  result 
  "distinctly 
  establishes 
  

   the 
  fact, 
  that 
  the 
  quantity 
  of 
  rain 
  which 
  flowed 
  off 
  by 
  the 
  sewers 
  was, 
  in 
  all 
  

   cases, 
  much 
  less 
  than 
  the 
  quantity 
  which 
  fell 
  on 
  the 
  ground," 
  also 
  "that 
  

   J 
  of 
  an 
  inch 
  of 
  rainfall 
  will 
  not 
  contribute 
  |^ 
  of 
  an 
  inch 
  to 
  the 
  sewers 
  ; 
  

   nor 
  a 
  fall 
  of 
  -j^y 
  of 
  an 
  inch 
  more 
  than 
  J 
  of 
  an 
  inch." 
  

  

  Again: 
  " 
  As 
  it 
  would 
  not 
  have 
  been 
  wise 
  or 
  practicable 
  to 
  have 
  increased 
  

   the 
  sizes 
  of 
  the 
  intercepting 
  sewers 
  much 
  beyond 
  their 
  present 
  dimensions 
  

   in 
  order 
  to 
  carry 
  off 
  the 
  rare 
  and 
  excessive 
  thunderstorms, 
  overflow 
  sewers, 
  

   to 
  act 
  as 
  safety 
  valves 
  in 
  times 
  of 
  storms, 
  have 
  been 
  constructed 
  at 
  the 
  

   junctions 
  of 
  the 
  intercepting 
  sewers 
  with 
  the 
  main 
  valley 
  lines." 
  

  

  Again 
  : 
  " 
  Having 
  determined 
  the 
  quantities 
  of 
  sewage 
  and 
  rainfall 
  to 
  be 
  

   carried 
  off, 
  and 
  the 
  rate 
  of 
  declivity 
  of 
  the 
  sewer 
  required 
  for 
  the 
  necessary 
  

   velocity 
  of 
  flow, 
  the 
  sizes 
  of 
  the 
  intercepting 
  sewers 
  were 
  readily 
  determined 
  

   by 
  the 
  formulae 
  of 
  Prony, 
  Eytelwein, 
  and 
  Du 
  Buat." 
  

  

  Again 
  : 
  "A 
  primary 
  object 
  sought 
  to 
  be 
  attained 
  in 
  this 
  scheme 
  was 
  

   the 
  removing 
  as 
  much 
  of 
  the 
  sewage 
  as 
  practicable 
  by 
  gravitation, 
  so 
  as 
  to 
  

   reduce 
  the 
  amount 
  of 
  pumping 
  to 
  a 
  minimum." 
  Under 
  this 
  view, 
  on 
  the 
  

   north 
  side 
  of 
  the 
  Thames, 
  the 
  high 
  level 
  sewer 
  commences 
  at 
  the 
  foot 
  of 
  

   Hampstead 
  Hill, 
  passing 
  through 
  certain 
  districts 
  of 
  London, 
  draining 
  about 
  

   ten 
  square 
  miles 
  (shown 
  in 
  the 
  plan), 
  the 
  form 
  of 
  which 
  "is 
  mostly 
  cu-cular, 
  

   and 
  it 
  varies 
  in 
  size 
  from 
  4 
  feet 
  in 
  diameter 
  to 
  9 
  feet 
  6 
  inches 
  by 
  12 
  feet 
  ; 
  

   its 
  fall 
  is 
  rapid, 
  ranging 
  at 
  the 
  upper 
  end 
  from 
  1 
  in 
  71 
  to 
  1 
  in 
  376, 
  and 
  from 
  

   4 
  feet 
  to 
  5 
  feet 
  per 
  mile 
  at 
  the 
  lower 
  end." 
  

  

  The 
  middle 
  level 
  sewer 
  is 
  as 
  near 
  the 
  Thames 
  as 
  the 
  contour 
  of 
  the 
  

   ground 
  will 
  allow, 
  the 
  area 
  intercei^ted 
  being 
  17^ 
  square 
  miles. 
  

  

  The 
  low 
  level 
  sewer 
  intercepts 
  the 
  sewage 
  from 
  the 
  low 
  level 
  area, 
  which 
  

   contains 
  11 
  square 
  miles. 
  " 
  It 
  is 
  also 
  the 
  main 
  outlet 
  for 
  a 
  district 
  of 
  about 
  

  

  