300 



comparison of these two functions, viz. the efficiency expended on, 

 and the duty performed by, any machine, an exact measure of its 

 intrinsic work will be obtained. 



The author then proceeds to instance the utility of this new term 

 in investigating the mechanical value of the recoil-engine ; and by an 

 algebraic process, taking every thing most favourable to the engine, 

 arrives at the conclusion that the duty cannot, even in the best state 

 of its action, materially exceed half the efficiency, and that in con- 

 sequence it can never be used with advantage, the water-wheel and 

 the pressure-engine offering much greater duties ; while the wheel 

 possesses the advantage of preserving a uniformity of efficiency during 

 its whole action, which is not the case with the recoil-engine. And 

 these considerations lead him to remark on the impossibility of car- 

 rying into effect a plan proposed by some eminent engineers for ap- 

 plying steam on a principle of recoil. 



To estimate the efficiency of steam acting uniformly with its en- 

 tire force, the author assumes from experience that a bushel of coals 

 can convert into steam 14 cubic feet of water, occupying 1330 times 

 that space in the state of steam, and therefore lifting an atmosphere 

 incumbent on the surface of the water uniformly to 1330 times its 

 depth ; thus giving an efficiency of about 39 millions of pounds, 

 raised one foot high. From this he concludes (all deductions made), 

 30 millions would probably be the utmost attainable limit of duty, 

 but for two expedients ; 1st, causing the steam to act expansively, 

 after exerting its whole force through a certain part of the cylinder ; 

 2ndly, raising its temperature, by an increased expense of fuel, much 

 above 212. 



Both these means are considered, and occasion is taken to compare 

 the efficacy of the methods invented by Messrs. Watt and Hornblower 

 for the former purpose, the preference in point of simplicity and ad- 

 vantage being given however to the former. With regard to the 

 latter, it is concluded that in certain cases, advantage is really gained 

 by the use of strong steam. The author then alludes, with appro- 

 bation, to a method recently attempted, where a small quantity of 

 water is forced at each stroke into a minute boiler ; presenting, how- 

 ever, a very large surface, in proportion to its capacity, and kept at 

 an equable high temperature by immersion in fused metal. But he 

 considers the greatest hopes of increased power to rest on the appli- 

 cation to mechanical purposes of some fluid more elastic than the 

 vapour of water, according to the suggestion of the President, in the 

 Philosophical Transactions for 1823. 



The author concludes this paper by a statement of the duties ac- 

 tually performed by the engines in Cornwall ; from which it appears 

 that several of the large engines there at work are actually perform- 

 ing a duty greater than the whole efficiency of the steam, unaided by 

 expansive working or high pressure, on the assumptions here made ; 

 while others, apparently similar in every respect, fail of performing 

 half that duty, and no satisfactory cause has been assigned for that 

 important difference. 



