394 
ME.  FAIEBAIEN  ON  THE  EESISTANCE  OE  TTBES  TO  COLLAPSE. 
observed  that  the  tubes  being  screwed  to  the  covers  of  the  cylinder,  were  to  some  extent 
in  a state  of  tension,  ovdng  to  the  necessity  of  having  to  screw  up  the  air-tube  tight  in 
order  to  prevent  leakage.  This,  with  the  weakness  of  the  ends  of  the  first  two  tubes, 
will  account  for  the  discrepancies  in  the  Table.  Making  allowances  on  this  gi-ound  and 
taking  the  mean  of  the  experiments,  we  arrive  at  the  conclusion  that  the  results  approxi- 
mate closely  to  the  law  that  the  strengths  are  inversely  as  the  length ; and  this,  it  will  be 
observed,  is  the  result  arrived  at  in  the  comparison  of  the  4 -inch  tubes. 
Thus  the  mean  strength  of  the  tubes,  30  inches  long,  experiments  G,  H,  K,  L.  is 
53  lbs  per  square  inch.  Now  by  the  above  inverse  proportion,  we  may  calculate  fi-om 
this  the  strength  of  a tube  59  inches  long ; thus, 
59:30;:52:.r=27, 
the  result  being  32  in  the  above  Table,  Experiment  9,  a difference  of  5 lbs.  only. 
This  law  receives  remarkable  confirmation  from  Experiment  6 on  tube  F.  This  tube 
had,  as  already  explained,  two  rigid  cast-iron  rings  fii'mly  soldered  to  it  so  as  to  divide 
its  length  into  three  equal  parts.  The  result  was  to  increase  the  strength  threefold,  or. 
in  other  words,  to  make  it  equal  in  strength  to  a tube  of  one-thhd  the  length. 
The  next  series  of  tubes  submitted  to  experiment  were  8 inches  in  diameter,  and  of 
the  same  thickness  as  the  preceding.  In  these  experiments  it  will  be  seen  that  rhe 
same  law  in  respect  of  the  length  prevails,  and  is  perhaps  more  strikingly  exemplified 
than  in  either  of  the  preceding  series.  Perhaps  from  their  lai’ger  size  these  tubes  were 
less  affected  by  defects  of  workmanship.  Like  the  last,  they  had  an  outlet  for  the  escape 
of  the  air,  and  collapsed  with  loud  reports. 
Table  III.  Kesistance  of  8-inch  tubes. 
On  comparing  the  above  results,  it  will  be  found  that  there  is  a near  approximatioiij 
to  the  strengths  being  inversely  as  the  lengths.  Takmg  the  strength  of  the  fii'st  tubei 
30  inches  long,  and  calculating  the  force  necessary  to  collapse  the  39  and  40-inch  tubesJ 
we  have,  by  calculation,  ' 
39:  30:  : 39:  ^=30  and  40 : 30 ::  39  : 0.-29-25 ; j 
