ME.  FAIEBAIEN  ON  THE  EESISTANCE  OF  TUBES  TO  COLLAPSE. 
397 
Table  VI.  Eesistance  of  tubes  with  lap-  and  butt-joints. 
The  tube  Y,  Experiment  23,  was  made  with  a lap-joint,  which  caused  it  to  deviate 
from  a true  circle  in  form,  to  the  extent  of  nearly  a quarter  of  an  inch,  the  double 
thickness  of  the  plates.  In  the  tube  Z,  the  cylindrical  form  was  better  maintained  by 
the  butt-joint,  and  this  difference,  apparently  so  small,  had  a serious  effect  upon  the 
resisting  powers  of  the  tube.  According  to  the  results  in  the  Table,  there  was  a loss  of 
more  than  one-third  of  the  strength  in  the  tube  -with  the  lap-joint,  the  ratio  being 
69-3:100,  or  7: 10  nearly.  These  facts  are  conclusive  in  showing  the  necessity  of 
adhering  in  these  constructions  to  the  true  cylindrical  form. 
The  foregoing  experiments  were  instituted  for  the  pm-pose  of  ascertaining  the  resist- 
ance of  tubes  to  collapse,  when  the  ends  were  securely  fixed  to  unyielding  discs  (as  is  the 
case  with  the  flues  of  a boiler),  and  rigidly  kept  apart  to  prevent  their  approaching  one 
another.  In  this  position,  the  tubes,  when  submitted  to  severe  collapsing  pressures,  were 
to  some  extent  in  a state  of  tension,  and  in  some  few  cases,  when  collapse  took  place, 
the  sides  were  tom  from  the  cast-iron  discs. 
The  results  obtained  from  tubes  of  this  construction  have  ah'eady  been  recorded,  but 
we  have  yet  to  ascertain  to  what  extent  tubes  of  the  same  size  and  form  follow  the  same 
laws  in  their  resistance  to  external  pressure  when  their  ends  are  left  free  to  approach 
each  other.  To  solve  this  question  two  tubes  were  made,  similar  to  those  previously 
experimented  upon,  of  8 inches  diameter  and  60  and  30  inches  in  length.  In  these 
tubes  there  was  no  rigid  bar  down  the  centre,  nor  were  they  attached  to  the  cylinder 
covers ; they  were  simply  placed  in  the  cylinder,  and  -water  pumped  in,  in  the  usual 
manner,  until  they  collapsed  as  given  in  the  following  Table : — 
