114 
Steam Engine, 
Fig. 4, which is a section of the steam -pipes, taken at 
right angles to that in fig. 3, shews this more distinct!]/ j 
s is the pipe which conveys the steam from the boiler ; a 
and c are the steam- valves, and b and d the eduction^ 
valves. By attending to the operation in both the sections^ 
the reader will easily understand it. It appears at first a 
litt le confused, by there seeming to be only .one steam- 
pipe for communicating between the cylinder and the 
condenser ; but the difficulty is cleared up, by represent- 
ing both 'the pipes, as in fig. 4. 
Fig. 5, is a longitudinal section of the boiler, repre- 
senting the mode of supplying it with water, and the 
safety-valve and cocks, f is a small cistern, which is 
supplied with water from the hot-w^ell, as represented in 
fig. 3 ; from the bottom of this cistern, a pipe goes down 
almost to the bottom of the boiler, where it turns up a lit- 
tle, to prevent the entrance of the steam which rises from 
the bottom. From the side of this cistern, is support- 
ed a small lever, to one end of which is fastened a wire,, 
tliat carries a stone which hangs in the water of the boiler ; 
the other end of the lever supporting also by a wire, a 
valve that shuts the top of the pipe that goes down from 
the cistern. Now, suppposing the stone just at the sur- 
face of the water, and balanced by a weight at the oppo- 
site end of the lever ; it is evident, that by the laws of hy- 
drostatics, already explained, a certain part of the weight 
of the stone will be supported by the water, so long as it 
continues immersed in it ; but if a part of the w^ater evapo- 
rate by boiling, a proportional part of the stone will be 
above the water, consequently the stone will bear more 
upon the lever and raise the weight at the other end ; but 
in raising that weight, it also opens the valve in the small 
cistern, and admits water until it stand at the same height 
in the boiler as before, and then the valve and the stone 
being again in eqiiilibrio, the valve remains shut until a- 
