OF THE IRK, LOCOMOTIVE ENGINE. 507 
oecomes inverted, when the water in the boiler 
will be discharged immediately, at the top of the 
fire-box. 
From these circumstances, of the motion of the 
Engine and the force of the steam, the action of 
the steam would not be instantaneous; for, if it 
had been instantaneous, the engine would have 
been thrown upwards ; but, it could not have had 
any horizontal motion. 
When the fire-box end of the Engine has re- 
volved through 180’, the force of the steam will 
counteract the first horizontal motion of the Engine, 
and will impel it horizontally in an opposite direc- 
tion ; but, when the fire-box has revolved through 
180°, the water is discharged from the boiler, and 
no more steam can be generated. The Engine 
will, therefore, have acquired its greatest rotatory 
motion when it has revolved through 180°; and 
as this rotatory motion would be destroyed by im- 
pinging on the tie-beams, we may suppose, that 
the Engine had acquired its greatest horizontal 
velocity, before it struck the first tie-beam. 
8. A cubic foot of water weighs 1000 ounces 
avoirdupois; and, therefore, a cubic inch of water 
