40 THE SCIENTIFIC PAPERS OF 



3rd. The reabsorption of the waste heat was carried out to 

 greater perfection, by means of a series of thin iron plates, pre- 

 senting a very large aggregate surface, which were held a small 

 distance apart by fillets, to allow of the passage of air between 

 them. 



The lower extremities of these plates were heated by the fire to 

 about 650 Fahr., while the upper extremities were maintained at 

 the lowest possible temperature, by coils of cold-water pipes. 

 The air was made to pass to and fro between the same surfaces, 

 for every stroke of the engine, by means of a large displacing 

 plunger, which was not required to work tight in its cylinder. 

 In descending, the air absorbed heat, in the gradual proportion of 

 the increasing temperature of the plates, and in consequence its 

 elastic pressure was increased during ihe ascending stroke. By 

 the reverse process, a fall to the former temperature and a 

 decrease of pressure, inversely proportionate to the temperature 

 and the space occupied, was effected, which space was, in the 

 meantime, increased by the amount of the capacity of the working 

 cylinder. 



The opposite ends of the working cylinder communicated with 

 two distinct heating apparatuses, the displacing plungers of which 

 were attached to the opposite ends of a beam and made stroke, 

 while the working piston was on its dead centres. 



The excessive pressure of the heated air, beneath the one, over 

 the cold air above the other displacing plunger, constituted the 

 working pressure ; and the capacities of the displacing cylinders 

 had to be so proportioned to the working cylinder, that the work- 

 ing pressure was not exceeded by the resisting pressures at the end 

 of each stroke ; or supposing the volume of the air was doubled 

 by the heat, it follows, that the net capacity of each displacing 

 cylinder had to be equal to at least twice the capacity of the 

 working cylinder. 



Fig. 5, Plate 5, is a theoretical diagram of Stirling's engine ; 

 the curve a a a represents the entire expansion of the air, from 

 the time when it is all confined in the heated space, below the 

 displacing plunger, to the moment when it occupies the cold 

 extended space, above the displacing plunger, and the working 

 cylinder. The power due to this expansion is measured by the 

 field a a a x y z, and is equivalent to 123 units of heat, as shown 



