Notices of American Steam Boats. B15 
To this must be added the net pressure of the atmosphere, obtained 
by the use of the condenser and air-pump, which is fully equal to 
ten pounds to the inch, the vacuum in the condenser ranging gener- 
ally from twelve and a half to thirteen and a half pounds to the inch, — 
by the barometrical guage. This estimate whichis obtained by 
near approximations, will give an average pressure on the piston, 
equal to twenty pounds to the square inch; but lest we should be 
charged with overrating, we will reduce it 60 sixteen pounds, effective 
pressure to the square sit: on three thousand four hundred and 
twenty one inches of piston, running fifty two single strokes, of ten 
feet each, per minute. Estimating now the full power of a horse as 
equal to one hundred and fifty pounds, moving at two and a half miles 
an hour, or to raising thirty three thousand pounds one foot per 
tee 3421 x 16 x 52 x 10 
33.000 
, showing a force exerted upon the engine which 
‘minute, we have the following formula; 
— 28462720 _ ano 
ess000 
is equal to the power of eight hundred and sixty two horses. From 
this result we are to deduct the power necessary for moving the en- 
gine, or that Fequired for overcoming the friction and resistance of 
its parts, whic ngines of this magnitude, work- 
ing on such an extended crank, than j in the average of smaller engines. 
We will estimate it, however, as equal to one third of the force ap- 
. plied, which gives the effective working power of the engine as equal 
to that of five hundred and seventy five horses! An engineer with 
whom I have conferred, and under whose direction several of the 
_ engines in these boats have been constructed, estimates the net ef- 
fective pressure, exclusive of all deduction for friction, &c. as equal 
to twelve pounds for every square inch of the piston. ‘This may be 
‘hearer the truth, and gives the working power of this engine as equal 
to six hundred and forty six horses. Such results may at the on 
view appear to be of a startling character, even to 
teaders, but having been arrived at by gradual approximations, they 
seem hardly to have attracted the attention, either of men of science, 
or practical engineers. 
~The following may be given as a summary statement of the prin- 
cipal dimensions of the other boats which have been named, and 
which, if not minutely correct in all its particulars, is sufficiently so 
for purposes of general information. The Champlain, a new boat, 
is one hundred and eighty feet in length, twenty eight feet beam on 
