OF THE IRK, LOCOMOTIVE ENGINE. 509 
The large aperture, through which the steam is rapidly 
discharged, allowing this supposition 
A=,4=that of steam, the pressure of which is equal to 
that of the atmosphere. 
p=the pressure of the steam, in ounces, on one foot of the 
surface of a section of the steam, in the boiler, 
close to the orifice, at the time, t. 
v=the velocity with which the steam is moving, in the 
boiler, close to the orifice, at the time, ¢. 
a=11=the area of the orifice, in square feet. 
11=34560=the pressure of the atmosphere, in ounces, on 
a square foot. 
g=32} feet. 
Then, by Professor Moseley’s Hydrostatics 
and Hydrodynamics, Art. 195, the general ex- 
pression for the motion of an elastic fluid, is 
EP — AP x ude 
But, the action of gravity on the steam is so 
small, when compared with the force arising from 
the pressure of the steam, that P may be neg- 
lected ; and when p is diminished, »v is diminished 
also; therefore 
SP = vdy 
But, because, by Art. 8, the pressure of the 
steam varies as its density, 
3 Y 
