﻿Thomson. 
  — 
  On 
  the 
  Cleansing 
  of 
  Towns. 
  41 
  

  

  " 
  By 
  this 
  arrangement 
  the 
  sewage 
  is 
  not 
  only 
  at 
  once 
  dihited 
  by 
  the 
  

   large 
  volume 
  of 
  water 
  in 
  the 
  Thames 
  at 
  high-water, 
  but 
  is 
  also 
  carried 
  by 
  

   the 
  ebb 
  tide 
  to 
  a 
  point 
  in 
  the 
  river 
  twenty-six 
  miles 
  below 
  London 
  Bridge, 
  

   and 
  its 
  return 
  by 
  the 
  follo\ving 
  flood 
  tide 
  within 
  the 
  metropolitan 
  area 
  ia 
  

   effectuaUy 
  prevented." 
  

  

  Again 
  : 
  " 
  At 
  the 
  threshold 
  of 
  my 
  (Sir 
  J. 
  W. 
  Bazalgette's) 
  enquhy 
  into 
  

   this 
  subject 
  the 
  following 
  important 
  points 
  required 
  to 
  be 
  solved 
  : 
  — 
  

  

  "1st. 
  At 
  what 
  point 
  and 
  state 
  of 
  the 
  tide 
  can 
  the 
  sewage 
  be 
  discharged 
  

   into 
  the 
  river, 
  so 
  as 
  not 
  to 
  return 
  within 
  the 
  more 
  densely 
  inhabited 
  por- 
  

   tions 
  of 
  the 
  metropolis 
  ? 
  

  

  " 
  2nd. 
  What 
  is 
  the 
  minimum 
  fall 
  which 
  should 
  be 
  given 
  to 
  the 
  inter- 
  

   cepting 
  sewers 
  ? 
  

  

  "3rd. 
  What 
  is 
  the 
  quantity 
  of 
  sewage 
  to 
  be 
  intercepted, 
  and 
  does 
  it 
  

   pass 
  off 
  in 
  a 
  uniform 
  flow 
  at 
  aU 
  hours 
  of 
  the 
  day 
  and 
  night, 
  and 
  in 
  what 
  

   manner 
  ? 
  

  

  " 
  4th. 
  Is 
  the 
  rainfall 
  to 
  be 
  mixed 
  with 
  the 
  sewage 
  ? 
  In 
  what 
  manner 
  

   and 
  quantities 
  does 
  it 
  flow 
  into 
  the 
  sewers 
  ; 
  and, 
  also, 
  is 
  it 
  to 
  be 
  carried 
  

   off 
  in 
  the 
  intercepting 
  sewers, 
  and 
  how 
  is 
  it 
  to 
  be 
  provided 
  for 
  ? 
  

  

  " 
  5th. 
  Having 
  referred 
  to 
  all 
  these 
  points, 
  how 
  are 
  the 
  sizes 
  of 
  the 
  

   intercepting 
  and 
  main 
  drainage 
  sewers 
  to 
  be 
  determined 
  ? 
  

  

  " 
  6th. 
  What 
  description 
  of 
  pumping 
  engines 
  and 
  of 
  pumps 
  are 
  best 
  

   adapted 
  for 
  lifting 
  the 
  sewage 
  of 
  London 
  at 
  the 
  pumping 
  stations 
  ? 
  So 
  

   comprehensive 
  a 
  subject, 
  involving 
  not 
  only 
  the 
  above 
  but 
  many 
  other 
  

   important 
  topics, 
  cannot 
  be 
  fully 
  considered 
  within 
  the 
  limits 
  of 
  an 
  

   ordinary 
  paper, 
  in 
  which 
  these 
  questions 
  can 
  only 
  be 
  briefly 
  touched 
  

   upon." 
  

  

  Experiments 
  by 
  floats 
  were 
  now 
  made 
  on 
  the 
  river 
  Thames, 
  by 
  

   which 
  it 
  was 
  found 
  that 
  "the 
  excess 
  of 
  the 
  ebbs 
  over 
  the 
  floods 
  was 
  

   only 
  five 
  miles 
  in 
  four 
  days," 
  and 
  "that 
  a 
  substance 
  in 
  suspension, 
  works 
  

   'up 
  the 
  river 
  about 
  one 
  mile 
  a 
  day 
  at 
  each 
  high 
  water, 
  as 
  the 
  springs 
  

   strengthen, 
  and 
  down 
  the 
  river 
  two 
  miles 
  a 
  day 
  as 
  they 
  fall 
  off." 
  Again: 
  

   that 
  " 
  the 
  dehvery 
  of 
  the 
  sewage 
  at 
  high 
  water 
  into 
  the 
  river 
  at 
  any 
  

   point, 
  is 
  equivalent 
  to 
  its 
  discharge 
  at 
  low 
  water 
  at 
  a 
  point 
  twelve 
  miles 
  

   lower 
  down- 
  the 
  river 
  ; 
  therefore 
  the 
  construction 
  of 
  twelve 
  miles 
  of 
  sewer 
  

   is 
  saved 
  by 
  discharging 
  the 
  sewage 
  at 
  high 
  instead 
  of 
  at 
  low 
  water." 
  

  

  The 
  flow 
  of 
  sewage 
  in 
  the 
  drains 
  was 
  then 
  determined 
  by 
  reference 
  to 
  

   the 
  data 
  afforded 
  by 
  the 
  works 
  of 
  well-known 
  authorities, 
  and 
  it 
  was 
  con- 
  

   cluded 
  by 
  the 
  engineer 
  to 
  regard 
  that 
  "a 
  mean 
  velocity 
  of 
  one-and-a-half 
  

   miles 
  per 
  horn* 
  in 
  a 
  properly 
  protected 
  main 
  sewer, 
  when 
  running 
  half 
  

   full, 
  is 
  sufficient, 
  more 
  especially 
  when 
  the 
  contents 
  have 
  passed 
  through 
  

   a 
  pumping 
  station." 
  

  

  