42 THE SCIENTIFIC PAPERS OF 



surface, occasioned apparently from misapprehension of the 

 principle involved, it having been thought that the same heat 

 would serve over and over again to produce power, and that the 

 necessary expenditure of heat consisted only in the mechanical 

 loss by imperfect action of the respirative 'plates, which were 

 approached to each other to the utmost limits, consistent with an 

 unobstructed passage of the air. 



By the aid of the dynamical theory of heat it has been shown, 

 that there is another and far more important expenditure of heat 

 which should have been provided for. 



Another great practical defect in Stirling's engine, arises from 

 the necessity of providing a reservoir of highly-compressed air to 

 start with, and from the difficulty of preventing the escape of that 

 stock of air, through the stuffing-boxes, &c. 



Ericsson patented in 1851 another form of engine, which has 

 lately been executed on a gigantic scale and continues to excite 

 public attention. 



This engine, of which Fig. G, Plate 5, represents the theoretical 

 diagram, differs from the expansive air-engine (Fig. 4, Plate 5), 

 only in the application to it of Stirling's respirator, or regenerator, 

 and in the proportion between the capacities of the working and 

 pumping cylinder, which in his engine are as three to two. A is 

 the working cylinder, the bottom of which is made of wrought 

 iron, and exposed to the fire ; B is the pumping cylinder, which 

 draws in atmospheric air through the valve u and delivers it into 

 the air reservoir C through the valve v ; D is a slide valve, regulating 

 the admission of air to and from the working cylinders ; E is the 

 respirator, or regenerator (a box filled with wire gauze), which is 

 heated at the bottom by the fire, but is maintained cool towards 

 the upper end, by the alternate rush of cold air downwards. The 

 top of the working cylinder and the bottom of the pumping 

 cylinder are left open to the atmosphere, and the two pistons 

 are attached to the same rod by which motion is imparted to the 

 crank. 



The pressure in the air reservoir is said to be maintained at 

 10 Ibs. per superficial inch ( 25 Ibs. total pressure). In the 

 diagram, the figure a b c d e represents the entire pressure below 

 the 'working piston amounting to 28 Ibs. pressure per inch, up to 

 the point c, where the admission is supposed to be cut off, in order 



