526 
On Water and Air. 
[August, 
is a cylinder which is composed of Whitworth steel, which 
is enormously strong : we will place it in the hydraulic press, 
and subject it to the straining adtion. It may not at all 
succeed in the form of showing you the breaking of the 
metal, because the steel is so good that it may resist a force 
of ioo tons. There is a force of xo tons on it now, and we 
shall go on augmenting the pressure : 80 tons are now 
working upon that cylinder ; the gauge tells the story. You 
see what the heaping of small impulses will do— small in- 
crements of power. There is now a pressure of ioo tons to 
the square inch, and the steel has stood this test. That 
steel is not to be broken by that force. 
And now, having said so much, I have only to offer you 
my best thanks for the attention you have given me through- 
out this course of lectures. I do not know that I have ever 
given a course of lectures in this place that has gratified me 
more ; for I do not know that I have ever seen the young 
folks— the lads or the girls— more attentive than they have 
been during this course of lectures. I have to thank my 
excellent friend, Prof. Dewar; I have to thank Sir Joseph 
Whitworth ; I have to thank Prof. Abel ; and last, not least, 
I have to thank my excellent assistant, Mr. Cottrell. ' 
