]VIE.  FAIEBAIEN  ON  THE  EESISTANCE  OF  TUBES  TO  COLLAPSE. 
401 
one,  the  loss  being  much  greater  in  the  former  than  in  the  latter  case,  although  the 
ratio  of  the  diameters  is  about  the  same.  Allowance  must,  however,  be  made  for  inac- 
curacies of  construction,  though  we  might  reasonably  have  expected  a nearer  approxima- 
tion in  the  ratios  of  the  deficiency  of  strength.  From  these  facts,  however,  it  is  obvious 
that  in  every  construction,  where  tubes  have  to  sustain  a uniform  external  pressure, 
the  cylindrical  is  the  only  form  to  be  relied  upon,  and  any  departure  from  it  is  attended 
with  danger. 
Resistance  of  Tubes  to  Internal  Pressure. 
During  the  investigation  on  the  comparative  resisting  powers  of  tubes  to  collapse,  a 
question  arose  as  to  the  relative  powers  of  cylindrical  tubes  to  resist  an  internal  force 
acting  uniformly  over  their  sm^face.  It  has  already  been  demonstrated  that  the  resist- 
ance of  cylindrical  vessels  to  internal  pressure  varies  inversely  as  the  diameters,  but  what 
efiect  the  length  may  have  upon  the  strength  has  yet  to  be  determined.  We  have 
already  seen  that  a cylindrical  tube,  when  subjected  to  external  pressure,  loses  one-half 
its  strength  when  the  length  is  doubled,  and  so  on  in  other  cases ; hence  arose  the  inquiry, 
what  efiect,  if  any,  will  an  increase  of  length  have  upon  a tube  exposed  to  internal 
pressure  \ To  solve  this  problem,  three  tubes  of  precisely  the  same  diameter  and  thick- 
ness of  plates,  but  of  difierent  lengths,  were  prepared  and  submitted  to  experiment  as 
follows : — 
Table  XI.  Resistance  of  Tubes  to  Internal  Pressure. 
Mark. 
No. 
Diameter. 
inches. 
Length. 
inches. 
Thickness. 
inches. 
Pressure  of 
rupture, 
lbs.  per 
square  inch. 
Remarks. 
Cc. 
36 
6 
12 
•043 
475 
m. 
37 
6 
24 
•043 
235 
Ee. 
38 
6 
30 
•043 
230 
F/. 
39 
6 
48 
•043 
375 
G^. 
40 
12-13 
60 
•043 
no 
Considerable  discrepancies  occur  in  the  experiments  on  internal  pressure,  as  in  each 
case  the  tube  gave  way  at  the  riveted  joint.  Every  precaution  was  taken,  by  carefully 
brazing  them,  to  render  them  as  nearly  uniform  in  strength  as  possible.  The  weakness 
of  these  joints  was,  however,  very  apparent,  and  the  results  are  in  accordance  with  those 
arrived  at  several  years  previously,  when  it  was  found  that  the  strengths  of  riveted  plates 
were  as  the  numbers — 
100,  for  the  solid  plate  ; 
70,  for  the  double-riveted  joint ; 
56,  for  the  single-riveted  joint. 
3 H 2 
