THE STEAM ENGINE. 



1. WHET* the prodigious impetus given to civilisation all over 

 the world, during the last hundred years, by the invention and 

 improvement of the steam-engine is considered, and when it is 

 observed that this, so far from being a temporary influence, is one 

 that has constantly gone on, and still goes on with augmented and 

 vastly accelerated energy, 



Mobilitate viget viresque acquirit eundo, 



it cannot be matter of surprise, that every one endowed with the 

 most moderate gifts of sense and intelligence, whatever may be 

 his position on the social scale, is animated with a strong desire to 

 obtain some knowledge of the extraordinary machine by which 

 results of such vast, enduring, and wide-spread importance have 

 been attained. 



Though comparatively few have the time, the inclination, or 

 the peculiar intellectual aptitude to follow out the details of the 

 mechanism of this great invention, as developed in its numerous 

 applications to the various arts of life, all who are by circum- 

 stances and education raised above the condition of the rudest 

 and most unskilled labourer have both the time and the mental 

 qualifications to acquire a general acquaintance with the machine, 

 and with the physical principles from which it derives its power. 

 To this large class we now address ourselves, and propose to 

 present them in a very brief compass with a general view of the 

 principle and mechanism of the steam-engine, confining ourselves 

 chiefly to those broad and general features which are common to 

 all varieties of the machine, and discarding for the present 

 such minute details of the mechanism as are applied only 

 in particular forms of steam-engine, and which, though often 

 admirable for ingenuity of design and contrivance, are neverthe- 

 less subordinate in interest when brought beside the larger 

 and more general views we now refer to. 



2. The steam-engine, whatever be its form or purpose, 

 consists of two essentially different parts ; the first, that in which 

 the steam is generated, and the second, that in which the steam is 

 worked. Although these taken together are essential to the per- 

 formance of the machine, thename steam-engine in its strictest sense 

 would signify only the latter, the former being called theboiler. 



3. Boilers vary much in magnitude, form, structure, and even 

 in material, according to the purpose to which they are applied, 

 and the circumstances under which they are used. There are, 

 however, certain characters common to all. 



Every boiler consists of a reservoir for the water and steam, and 

 a furnace with its appendages for the combustion of the fuel, the 

 heat evolved from which is the physical agency by which th 



iicn the 



