Proceebinos of the Polytechnic Associatiox. 950 



bers present, and stated tliat he expected that the evening M'onh:! be 

 occupied by others, and lie had, therefore, not prepared either a paper 

 or an address, but, on a subject in which he wa8 so much interested, 

 lie would try to make a few remarks. He continued : 



Too many persons think of a steam enn-jne as a greasy machine, 

 requiring the attendance of a greasy mechanic, and too few realize 

 that to i>roperly understand its principles, and the best method of it3 

 construction, requires a tlnn-ough kiiowledge of some of the most 

 important branches of dynamical science. It does not follow, how- 

 ever, that a good steam engine can be built by a mere theorist, for 

 the very extreme to which theories of limited application have been 

 carried by some parties, has done much to liinder true improvement. 

 So, on the other hand, the mere mechanic makes little or no progress, 

 for as well might we expect a greater delivery of fluid from a crooked, 

 fanciful shaped pipe than from a straight one, as to anticipate any 

 real economy in changing the mere shape of a steam engine, or even 

 in the nse of many of the ingenionsly constrncted valve and varie- 

 ties of valve gear. To improve the steam engine requires, first, a 

 practical knowledge of its details and their operation, and, second, a 

 scientific knowledge of the laws relating to heat and its applications. 

 The results of practical experiments, properly compared and classified, 

 add to the stock of scientific information, and it has, in this way, 

 been found that the results due to theory are often so modified by 

 conditions and circumstance, as to be of little practical value. A 

 further inquiry to ascertain the reasons for the observed fiicts has, 

 however, in many cases, suggested remedies which would insure vciy 

 nearly the results expected. 



Few subjects have excited more discussion than that of the expan- 

 sion of steam, and inquiries are continually being made as to what is 

 the most economical point of cut off. It has been my privilege to 

 have been engaged for the U. S. Government, at the Novelty iron 

 works in this city, for a number of years in experiments to settle 

 these points ; and, although the oflEicial report has not been i)ub]is]ied, 

 I may say, without im[)ropriety, that there is no one ])()iiit where it 

 is most economical to cut off the steam, for the ]ioint of greatest 

 economy is varied by every change in condition, but particularly by 

 variations in steam pressure. In fact, it would seem that the steam 

 pressure has more iwfluence upon the economy than the expansion. 

 The most economical point of cut off in a non-condensing engine 

 using 100 pounds of steam is about one-sixth of the stroke, and if a 



