JSfotices of American Steam Boats. 315 



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 which is 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 to sixteen pounds, effective 

 pressure to the square inch, 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 



, .1 r u • r 1 3421X16X52X10 



mmute, we have the lollowmg lormula ; 



^ 33.000 



28462720 



= 862, showing a force exerted upon the engine which 



33.000 



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 required for overcoming the friction and resistance of 

 its parts, which is comparatively less in engines of this magnitude, work- 

 ing on such an extended crank, than 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 

 nearer the truth, and gives the working power of this engine as equal 

 to six hundred and forty six horses. Such results may at the first 

 view appear to be of a startling character, even to professional 

 readers, 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 



