275 
Steam Engine . 
than it otherwise would. Where the tide rises at the tail of a 
common mill, this principle may be applied to great advantage, 
as the wheel in many situations, may be set two or three feet low- 
er than it commonly is, and by driving off the back water occa- 
sioned by the tide, the extra power which is gained by increasing 
the fall, will be much more than the loss of the water expended 
in drawing off the back water at high tide. 
Communications upon the subject of this improvement will be 
gratefully received, and immediately noticed by the subscriber, 
the patentee, of Newburyport, Massachusetts, or by Dr. Thomas 
P. Jones, Philadelphia. 
JACOB PERKINS, 
STEAM ENGINE BOILER, 
WITH A PLATE. 
Sir — -As steam engines are becoming much in use through- 
out the United States, every thing that will tend to their improve- 
ment in working, or in saving of fuel, ought to be made public. 
With this view I have taken the liberty of making a rough sketch 
of one of the boilers which has been in use upwards of ten years 
at the water works in Philadelphia, for your inspection. After 
giving every attention in ascertaining the effect of three different 
sorts of boilers in that work, for several years, I am fully persuaded, 
that it far exceeds any boiler now in use at the water works, or any 
other which has come under my notice, both in saving fuel and 
the ease with which the steam can be kept up. This boiler is, 
and always has been, defective, by its having a wooden case, 
which cannot be kept sufficiently tight ; and, with this great defect, 
it does not burn so much fuel as the others with cast iron cases, 
which have the fire under their bottoms, with flues passing through 
and around them. The present drawing contemplates a cast iron 
case, which would be durable, and, no doubt, last fifty or sixty 
years, as it is not exposed to the heat of the fire. However , an 
objection may be made to its expense, I am well persuaded that if 
tho$e who have engines built, knew the value of a boiler of this 
sort, 50 per cent, advance in the first cost would be no object to 
them, as they would save far more than the difference long before 
the boiler would be worn out, 
