Prime Movers. 21 



pass. The air which left the working cylinder at a high, tem- 

 perature imparted to the wire gauze most of its heat, and this 

 was taken up by the air passing through it to the working 

 cylinder ; that side of the regenerator which was next the 

 latter being always very hot, and that at which the cold air 

 entered being always comparatively cool. The excess of pres- 

 sure on the piston in the working cylinder, above that on the 

 piston in the supply cylinder, constituted the power. When 

 the air was heated to 480° its volume was doubled, so that the 

 pressure per inch on each piston was the same ; but as one of 

 them had twice the surface of the other, it was acted on by a 

 double pressure. It was asserted that, with this arrangement, 

 only one-tenth of the entire heat was wasted. But any appa- 

 ratus, capable of depriving steam, or air, of its heat, in transitu, 

 must retard its progress, and therefore must diminish its effect. 

 The bad conducting power of air must cause it to absorb or 

 relinquish heat slowly, and with difficulty. And the cylinders 

 required are enormous : in Ericsson's sixty -horse engine, the 

 larger were six feet in diameter ; and in his marine engine, 

 fourteen. 



The extraordinary force exerted by electro-magnets, sug- 

 gested electro-magnetism as a moving power. The writer of 

 this article, some years ago, made a great number of experi- 

 ments on this subject;* and he was led to the conclusion 

 that certain properties, winch he had found in combinations of 

 electro-magnets, would always prevent their application in any 

 useful way. All the experiments that have since been made 

 with them, have established the soundness of the reasons on 

 account of which he abandoned the attempt. A superficial 

 view of the matter would lead to the impression that an 

 electro-magnetic engine must be more efficient than a steam- 

 engine of equal cost. But the expensive nature of the material 

 it consumes, the complication of its machinery, the diminution 

 of its power, by circumstances which cannot be avoided ; and 

 in many cases the uncertainty — we might almost say the capri- 

 ciousness — of its action, must ever leave it very inferior to 

 the steam-engine. And its warmest advocates have long since 

 acknowledgedf that, on the score of economy, electro-mag- 

 netism can never compete with steam. Indeed, the French 

 Government, when it offered a prize of £2000 for a successful 

 electro-magnetic engine, required only that it should not con- 

 sume more than half a kilogramme, or about seventeen and 

 a-half ounces, of zinc per horse-power per hour : in France 

 this would cost tenpence, in England less, but much more than 

 the same amount of steam-power. It is not difficult to show 



* See Eeports of the British Association for 1835, 1836, etc 

 t Page's Letter to the Government of the United States in 1850. 



