106 THE ADDRESSES, LECTURES, ETC., OF 



apparent mystery of the air-engine by the prevailing material 

 theory of heat ; and it must be recorded, I think, as a fact highly 

 creditable to the Council of the Institution of the day, that 

 notwithstanding my seeming heresy, the Telford medal was 

 awarded me for my paper, and was withheld from my competitors. 



In my paper above referred to, I gave experimental information 

 regarding the limits of efficiency of the economiser, respirator, 

 recuperator, or regenerator (by whichever term it may be most 

 acceptable), whilst I purposely abstained from mixing up with my 

 subject a description of the regenerative steam engine and con- 

 denser, which had enabled me to collect that information, and 

 which was certainly the first, and remains almost the only serious 

 attempt to realise the dictates of the dynamical theory of heat. 

 This engine was conceived in 1845, and at a time when the 

 writings of Carnot and Mayer had only just prepared the way for 

 Joule to determine experimentally the mechanical equivalent 

 of heat, and was constructed in 1846-7 by Messrs. Benjamin 

 Hick and Son of Bolton, at whose works it was in operation for some 

 time ; it was described, moreover, in a somewhat modified form in 

 my patent of 1847, No. 12,006, and is, I think, in some respects 

 worthy of notice in such a review as that with which you are now 

 presenting your readers. 



The leading ideas attempted to be realised in this engine are : 



1. That heat is force, and that the engine itself is only a 

 contrivance for giving the force of heat another direction. 



2. That the medium employed for effecting this change is, 

 theoretically speaking, immaterial, and that steam is preferable 

 to air because its coefficient of expansion is greater than that of 

 air, and that it can be brought back to its lowest temperature or 

 point of saturation by bringing it into contact with water of the 

 same temperature. The portion of the apparatus where this was 

 effected was called by me the regenerator, a term which has since 

 been applied to the mere exchanger of heat, which I at that time 

 called the respirator. 



3. That the amount of the elastic fluid employed in effecting a 

 stroke of the working piston or plunger must be reduced to a 

 minimum, because loss of heat arises in bringing the elastic 

 medium back to its original condition of compression after expan- 

 sion at elevated temperature. 



