ME.  FAIEBAIEN  ON  THE  EESISTANCE  OE  TUBES  TO  COLLAPSE. 
413 
Figui'e  1,  Plate  XXIX.,  exhibits  an  ordinary  boiler  flue,  30  feet  long  and  2 feet  9 
inches  in  diameter,  with  simple  lap-joints,  as  hitherto  invariably  constructed.  To  attain 
nearly  three  times  the  strength  of  this,  it  will  only  be  necessary  to  introduce  two  strong, 
rigid,  angle-iron  ribs,  as  exhibited  in  flgs.  2 and  3,  at  a,  a.  This  arrangement  will  not 
only  remove  all  doubts  as  to  the  strength  of  these  flues,  by  bringing  them  within  the 
limits  to  which  the  formula  applies  with  strictness,  but  will  give  to  flues  30  feet  long  a 
strength  equivalent  to  that  of  flues  only  10  feet  long,  and  make  them  uniform  in  their 
powers  of  resistance  with  the  other  parts  of  the  boiler. 
The  reduction  of  the  strength  of  flues  by  the  lap-joints  has  aheady  been  stated ; the 
deviation  from  the  true  cylindrical  form  which  they  cause,  lessens,  in  some  cases, 
seriously  the  strength  of  the  vessels,  as  may  be  seen  in  Experiments  23  and  24,  Table  VI. 
Hence  it  is  also  proposed  that  flues  requh’ed  to  resist  an  external  pressm-e  should  be 
formed  with  double-riveted  butt-joints,  with  longitudinal  covering  plates,  as  shown  at 
b,  b,  b,  fig.  3,  Plate  XXIX,  It  is  believed  that  these  alterations  will  secure  ample  safety 
in  these  important  constructions,  and  in  this  trust  they  are  commended  to  the  attention 
of  the  engineer  and  the  public  generally. 
