﻿42 
  Mr. 
  W. 
  H. 
  Macaulay 
  on 
  the 
  Stresses 
  

  

  the 
  rate 
  of 
  lieat-conduction 
  at 
  atmospheric 
  pressure 
  is 
  the 
  

   same 
  as 
  in 
  my 
  own 
  experiment 
  with 
  air 
  in 
  the 
  large 
  bulb, 
  and 
  

   illustrated 
  in 
  PL 
  II. 
  The 
  first 
  five 
  stations 
  in 
  the 
  curve 
  are 
  

   the 
  ones 
  from 
  which 
  they 
  deduced 
  their 
  " 
  Sixth 
  Law 
  " 
  of 
  

   cooling. 
  The 
  rest 
  of 
  the 
  curve 
  is 
  drawn 
  in 
  accordance 
  with 
  

   that 
  law, 
  and 
  the 
  vacuum 
  line 
  represents 
  exactly 
  the 
  value 
  

   they 
  assigned 
  to 
  the 
  cooling 
  power 
  of 
  an 
  absolute 
  vacuum. 
  

   Comparison 
  with 
  PI. 
  II. 
  shows 
  how 
  much 
  they 
  erred 
  in 
  their 
  

   deductions. 
  

  

  PL 
  X. 
  embodies 
  the 
  results 
  obtained 
  with 
  a 
  mixture 
  of 
  

   three 
  volumes 
  of 
  hydrogen 
  and 
  five 
  volumes 
  of 
  carbon 
  dioxide 
  

   in 
  the 
  small 
  bulb. 
  A 
  study 
  of 
  this 
  curve 
  in 
  connexion 
  with 
  

   PL 
  VI. 
  shows 
  that 
  the 
  carbon 
  dioxide 
  interfered 
  very 
  greatly 
  

   with 
  the 
  performance 
  of 
  the 
  hydrogen. 
  Before 
  any 
  exhaustion 
  

   was 
  made, 
  the 
  hydrogen 
  alone 
  would 
  have 
  done 
  more 
  than 
  

   three 
  times 
  the 
  work 
  of 
  both 
  gases. 
  It 
  was 
  not 
  until 
  the 
  

   pressure 
  had 
  fallen 
  to 
  about 
  one 
  hundred 
  millionths 
  that 
  both 
  

   gases 
  combined 
  did 
  as 
  well 
  as 
  the 
  hydrogen 
  would 
  have 
  done 
  

   alone. 
  Below 
  this 
  pressure 
  both 
  gases 
  contributed 
  to 
  the 
  

   result. 
  

  

  This 
  interference 
  of 
  mixed 
  gases 
  is 
  a 
  very 
  interesting 
  phe- 
  

   nomenon, 
  and 
  seems 
  to 
  warrant 
  the 
  careful 
  investigation 
  

   which 
  it 
  is 
  my 
  intention 
  to 
  give 
  it. 
  

  

  IT. 
  The 
  Stresses 
  and 
  Deflection 
  of 
  Braced 
  Girders. 
  - 
  

   Bi/W. 
  H. 
  Macaulay* 
  

  

  A 
  STRUCTURE 
  consisting 
  of 
  a 
  number 
  of 
  bars 
  hinged 
  

   together 
  (or 
  pin-jointed) 
  at 
  their 
  ends 
  is 
  called 
  a 
  frame. 
  

   The 
  points 
  at 
  which 
  hinges 
  occur 
  are 
  called 
  joints. 
  A 
  

   frame 
  is 
  said 
  to 
  be 
  stiff 
  if 
  the 
  number 
  and 
  arrangement 
  of 
  

   bars 
  are 
  such 
  that 
  the 
  frame 
  cannot 
  be 
  distorted 
  without 
  

   stretching 
  one 
  or 
  more 
  of 
  them. 
  If 
  this 
  is 
  not 
  iha 
  case 
  it 
  is 
  

   said 
  to 
  be 
  loose. 
  A 
  frame 
  is 
  said 
  to 
  be 
  just 
  stiff, 
  if 
  it 
  is 
  stiff 
  

   and 
  the 
  removal 
  of 
  any 
  one 
  bar 
  could 
  make 
  it 
  loose. 
  If 
  a 
  

   frame 
  is 
  stiff, 
  but 
  not 
  just 
  stiff, 
  it 
  is 
  possible, 
  by 
  removing 
  a 
  

   set 
  of 
  one 
  or 
  more 
  bars, 
  to 
  make 
  it 
  just 
  stiff 
  without 
  depriving 
  

   it 
  of 
  any 
  joints 
  ; 
  such 
  bars 
  are 
  called 
  redundant 
  bars. 
  A 
  frame 
  

   may 
  have 
  more 
  than 
  one 
  set 
  of 
  redundant 
  bars, 
  that 
  is 
  to 
  say 
  

   it 
  may 
  be 
  possible 
  to 
  reduce 
  it 
  to 
  being 
  just 
  stiff, 
  without 
  loss 
  

   of 
  joints, 
  in 
  more 
  than 
  one 
  way. 
  The 
  same 
  terminology 
  may 
  

   be 
  applied 
  to 
  a 
  frame 
  in 
  one 
  plane 
  ; 
  it 
  is 
  then 
  assumed 
  that 
  

   no 
  distortion 
  is 
  admissible 
  except 
  in 
  that 
  plane, 
  and 
  that 
  any 
  

   forces 
  applied 
  to 
  the 
  frame 
  are 
  in 
  its 
  plane. 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  