946 TuAKSAcnoxs of the American Institute. 



both condensing and non-condensing engines of all the usual styles 

 is very much wanted. The table gives the performance, in these 

 respects, of two of what were supposed, by their respective exhibi- 

 tors, the best and most economical engines in this country ; and the 

 results, as far as they reach, go to raise the reputation of the few 

 ancient dotards who continue to hold the opinion that the expansive 

 principle is of no practical value whatever in steam engineering. In 

 a discussion in the Mechanics' Chib last winter, a long and well- 

 written essay was read, from the pen of one of our oldest and most 

 practical engineers, arguing against the expansive nse of steam by 

 any possible arrangement. The author of that paper contended that 

 the supposed gain by expansion was all fallacious, and that all engines 

 would perform with maximum economy if they were constructed 

 Avith liberal openings, quick acting valves, little clearance, &c., and 

 receive steam at full pressure throughout the entire stroke of the 

 piston. The argument was received with the coldest kind of courtesy 

 by the majority of the members ; but the fact was developed that 

 several present cherished the same views, and, in short, that a consid- 

 erable minority of pureh'^ practical mechanics and engineers considered 

 the ordinaril^^ received law of hyperbolic logarithms a very ridiculous 

 hnmbug. It is hardly necessary to say, that the truth lies somewhere 

 in the broad space between these parties. There is a gain by the use 

 of steam expansively under almost any circumstances, unless the 

 principle is carried too far ; but the gain due to this is never, nnder 

 even the most favorable circumstances, quite equal to the rule on 

 which it is generally calculated. Multiplying the direct effect of the 

 steam at full pressure by the hyperbolic logarithm of the ratio of 

 expansion, plus one, gives a larger estimate of the effect of expansive 

 steam than is realized by any engine, either in Cornwall or out- 

 side of that almost fabulously economical locality. Besides 

 assuming the temperature of the steam to be maintained at 

 the initial point, which is notoriously impracticable even if the 

 weakened fluid be allowed to absorb heat through the sides of 

 the cylinder from a jacket of steam at full pressure outside, the 

 expansive use of steam is always too much interfered with by the 

 slow shutting of the steam valve, by other defects in mechanism, 

 and by the necessary increase of friction of the engine, to allow the 

 perfect realization of all the gain which theory, or rather which 

 false theory^ assigns to it. If Lord Bacon's experimentum crusis, 

 could be fairly applied to the expansive use of steam under some six or 



