of Edinburgh, Session 1879 - 80 . 575 
Thus the diminution per unit volume of the interior of the cylinder is 
2 (~ + ' 
When II is a ton- weight per square inch, the value of the quantity 
is somewhere about xwoo f 0 ! ordinary specimens of flint glass, and 
about xoVo f° r steel. 
It is ohyious from the formulse above, from which we have 
that the greatest of the three compressions is that perpendicular to 
planes through the axis, while the least is radial. The former has 
its maximum 
at the inner surface where, therefore, the tube will first yield to 
crushing ; the latter has its maximum at the outside. Their sum is 
constant. 
If we compare two tubes with the same internal bore, 5 mm , hut 
one two millimetres thick while the other is only half a millimetre, 
the maximum distortions under the same pressure are as f-J to 
or 4:9 nearly. 
When the pressure is internal we have 
and the increase per unit volume of the interior is 
In very thick tubes of narrow bore this is roughly — , the value of 
which in glass is about yxVo on ly f° r one ton pressure. 
