78 COKEELATION OF PHYSICAL FORCES. 



is argued you have a large amount of fuel consumed to raise 

 water to the boiling point, at which its efficiency as a motive 

 agent commences. After it has done a small portion of work, 

 and while it still retains a very large portion of the heat ori- 

 ginally communicated to it, you reject it, and have to start 

 again with a fresh portion of steam which has similarly ex- 

 hausted fuel in other words, you throw away all, and more 

 than all the heat which has been employed in raising the 

 water to the boiling point. Various plans have been de 

 to remedy this. Using again the warm water of the conden- 

 ser to feed the boiler regains a part, but a very small part, of 

 the heat. Employing the steam first for a high pressure, and 

 then before its rejection or condensation using it for a low 

 pressure, cylinder, is a second mode ; a third is to use the 

 .steam, after it has done its work on the piston, as a source of 

 heat or second furnace, to boil ether, or some liquid which 

 evaporates at a lower temperature than water. These plans 

 have certain advantages ; but the complexity of apparatus, 

 the danger from combustion of ether, and other reasons, 

 liave hitherto precluded their general adoption. Under the 

 term regenerating engine various ingenious combinations 

 have lately been suggested, and some experimental engines 

 tried, witli what success it is perhaps too early at present to 

 pronounce an opinion. The fundamental notion on which 

 this class of engine is based is that the vapour or air, when 

 it has performed a certain amount of work, as by raising a 

 piston, should, instead of being condensed or blown off, be 

 retained and again heated to its original high temperature, 

 and then used de novo; or that it should impart its heat to 

 some other substance, and the latter in turn impart it to the 

 fresh vapour about to act. The latter plan has been proposed 

 by Mr. Ericsson : he passes the air which has done its 

 work through layers of wire gauze, which are heated by the 

 rejected air, and through which the next charge of air is 

 made to pass. M. Seguin and Mr. Siemens have construct- 



