506 ON THE EXPLOSION OF THE BOILER 
vertical, the motive force of the steam to raise 
the centre of gravity of the Engine, will then 
become nothing; and after the plane of the top 
of the fire-box, has revolved through more than a 
right angle, the motive force of the steam will 
press the centre of gravity of the Engine down- 
wards. The Engine would, therefore, soon begin 
to descend ; and we will, therefore, suppose that 
the vertical force, with which the Engine impinges 
upon the tie-beams, is so small, that it may be 
neglected. Hence, then, we may suppose, that 
all the tie-beams were broken by the horizontal 
impact of the Engine; and we may calculate, 
what must be the force of the steam, so that all 
its force may be expended in breaking loose from 
the Tender, and in breaking the six tie-beams. 
As the fire-box end of the Engine will begin 
immediately to revolve about the centre of gra- 
vity of the Engine, and as it is supposed that 
there was very little water on the top of the fire- 
box, at the time of the explosion, there will not be 
any immediate discharge of water from the boiler 
into the fire-box ; and the water in the boiler 
being very hot, and there being nothing to dimi- 
nish the heat in the fire-box, steam will continue 
to be generated, until the position of the fire-box 
