20 Prime Movers. 



liable to tile objections which are fatal to that we shall con- 

 sider next. 



It was expected, that not only might a vacuum be produced 

 by explosive gases, but that a motive power also might be 

 directly obtained from it. The ignition-gas engine, which was 

 intended to carry out this object, was invented many years 

 since, and was re-invented about five years ago in America. It 

 is at present being tried as a new invention in France, by M. 

 Lenoir. — An explosive mixture, consisting of hydrogen, or 

 some of its compounds, and common air, is ignited by electricity 

 or other means, in a cylinder, the piston of which is impelled by 

 the expansion and subsequent contraction produced by combus- 

 tion. One measure of hydrogen and two and a-half of common 

 air expand, during explosion, to three times, and then collapse 

 to one-half, of their original bulk. Several years since, this 

 engine was characterized as " violent, vacillating, and noisy," 

 and it must necessarily be so. Such a principle cannot be 

 successfully applied ; the inertia of matter renders it impossible 

 for machinery to be effectually moved by sudden and transient 

 impulses, such as those which are the result of explosions. To 

 move a material substance, particularly if it is of considerable 

 weight, the power must continue to act upon it for some appre- 

 ciable time. Even gunpowder may be so manufactured as to 

 explode too rapidly for the production of a proper effect on the 

 ball. A door, which may be easily closed by gently pushing it 

 with the finger, will move very little, or not at all, when struck 

 suddenly or violently with the hand ; and, the more violent the 

 blow, the less it will move. Other explosive mixtures, including 

 gunpowder, have been tried, with similar results. 



The substitution of heated air for steam was proposed, in 

 1816, by Stirling ; and, about twenty-five or thirty years ago, 

 air, expanded in an iron cylinder, which was kept at a red heat, 

 was used for giving motion to a piston. But, as in all the 

 experiments of this kind which have been made, it was found 

 that the cylinder was soon destroyed by the high temperature. 

 In Ericsson's caloric engine, which was constructed on this 

 principle, and caused so much excitement some time ago, in 

 America, there were two larger and two smaller cylinders — 

 a smaller being placed above a larger, and the pistons of both 

 being made to move together. The air passed from the 

 smaller or supply cylinder, through a regenerator, where it was 

 heated to about 450°, to the larger or worhing cylinder, where 

 its temperature was raised to 480°, by a fire placed underneath. 

 The regenerator — to which the name of respirator was given, 

 in the regenerative steam-engine, mentioned above — was a vessel, 

 in which sheets of wire gauze were placed side by side, so as 

 to form innumerable cells, through which the air was made to 



