50 Perkins'' Steam Engine. 



piston has descended through one-eighth of its stroke, the in- 

 gress of steam is shut off and the other seven-eighths of the 

 stroke is performed by expansion. 



Mr. Perkins' original idea of substituting pressure for sur- 

 face, in generating steam, (which appears to be the basis of 

 his invention,) has never for a moment been abandoned ; 

 and the invention, if satisfactorily established, must certainly 

 be considered as of the utmost importance, particularly in 

 its first feature, absolute safety, which could hardly have been 

 contemplated in any other plan of boiler, to the extent which 

 this construction evidently exhibits the capability of effecting. 

 From the mode of constructing the compound generator as 

 now adopted, it becomes a safety valve of itself ; for the 

 pressure is divided into so many compartments, that any one 

 of them may explode with impunity, without even disturbing 

 a brick of the furnace. Although in the early part of the 

 invention, many explosions took place, without any attending 

 accident, (which served to show the safety of this method of 

 generating steam, as well as to point out the proper way of 

 constructing the generators,) yet for the last two years, it is 

 said that nothing of the kind has taken place, notwithstanding 

 the steam has been frequently raised to a pressure of above 

 1500 lbs. to the square inch. 



To illustrate the safety of this method of generating steam, 

 let us imagine a few tons of gunpowder to be confined with- 

 in one compartment, and if ignited, the tremendous effect 

 will be readily anticipated ; but let this same quantity of 

 powder be divided into a proper number of compartments, 

 and any one coversant with fire works, would not hesitate to 

 explode it with a match, of not more than a few inches in 

 length. We should not have dwelt so long on this part of 

 the invention, had not the alarm,, from the great number of 

 explosions within the last year or two, not only in this coun- 

 try, but in France and America, created universal terror ; 

 particularly in steam boat travelling ; and the danger of ex- 

 plosion would still be more alarming, since it has been re- 

 cently discovered that the safety valve is of no use, when 

 an explosion takes place from the sudden generation of 

 steam. 



We will now mention some of the practical difficulties 

 which Mr. P. has had to contend with. First, the re-action 

 of this highly elastic steam on the eduction side of the pis- 

 ton, occasioned by its density, and expansive property. 



