MECHANICS AND USEFUL ARTS. 45 



pass into the working cylinder, to force up the working piston within 

 it. As it leaves the receiver to perform this duty, it passes through 

 what is called the regenerator, which we shall soon explain, where it 

 becomes heated to about four hundred and fifty degrees, and upon 

 entering the working cylinder, it is further heated by the fire under- 

 neath. We have said the working cylinder is much larger in 

 diameter than the supply cylinder. Let us, for the sake of illustration 

 merely, suppose it to contain double the area. The cold air which 

 entered the upper cylinder will, therefore, but half fill the lower one. 

 In the course of its passage to the latter, however, we have said that 

 it passes through a regenerator, and let us suppose, that as it enters 

 the working cylinder, it has become heated to about four hundred 

 and eighty degrees. At this temperature, atmospheric air expands to 

 double its volume. The atmospheric air, therefore, which was con- 

 tained within the supply cylinder, is now capable of filling one of 

 twice its size. With this enlarged capacity it enters the working 

 cylinder. We will further suppose the area of the piston within this 

 cylinder to contain a thousand square inches, and the area of the 

 piston in the supply cylinder above, to contain but five hundred. 

 The air presses upon this with a mean force, we will suppose, of 

 about eleven pounds to each square inch ; or in other words, with a 

 weight of 5,500 pounds. Upon the surface of the lower piston, the 

 heated air is, however, pressing upward with a like force upon each 

 of its one thousand square inches ; or, in other words, with a force 

 which, after overcoming the weight above, leaves a surplus of 5,500 

 pounds, if we make no allowance for friction. This surplus furnishes 

 the working power of the engine. It will be readily seen that, after 

 one stroke of its pistons is made, it will continue to Avork with this 

 force, so long as sufficient heat is supplied to expand the air in the 

 working cylinder to the extent stated ; for, so long as the area 

 of the lower piston is greater than that of the upper, and a like 

 pressure is upon every square inch of each, so long will the greater 

 piston push forward the smaller, as a two pound weight upon one end 

 of a balance will be quite sure to bear down one pound placed upon 

 the other. We need hardly say, that after the air in the working 

 cylinder has forced up the piston within it, a valve opens, and as it 

 passes out, the pistons, by force of gravity, descend, and cold air 

 again rushes into, and fills the supply cylinder, as we have before 

 described. In this manner the two cylinders are alternately supplied 

 and discharged, causing the pistons in each to play up and down, sub- 

 stantially as thev do in the steam engine. 



*-^ 



The most striking feature of the Caloric Engine consists in what is 

 called the regenerator. Before describing this, we will present the 

 idea upon which it is based. First, let it be remembered that the 

 power of the steam engine depends upon the heat employed to pro- 

 duce steam within its boilers. It will be seen that from the very 

 nature of steam, the heat required to produce it, amounting to about 

 1,200, is entirely lost by condensation the moment it has once 

 exerted its force upon the piston. If, instead of being so lost, all the 



