Proceedixgs of the PoLYTECIiyiC ASSOCIATIOX. 951 



Tliere are many points of more or less interest ]»resented in tlie 

 first table, but M'aiit of space allows }iartieu]ar atteiit!(_)ii to be invited 

 to but one more ; the per centage of the mechanical e<piivalent actually 

 realized. The last column in the table brin^^-s out, in a very strong- 

 light, the broad margin which yet remains for improvement in the 

 use of heat as a means of generating power. ( )f all the heat produced 

 by a given quantum of lire, a large amount, from one-quarter to one- 

 half, escapes up the stack in the heated gases. The remainder pene- 

 trates the metal, and entering the water, comlnnes therewith, and 

 forms the steam, which rises and liows through the connections into 

 the cylinder, acts on the piston with full pressure tlu-ough a portion 

 of its travel, is then isolated (or '" cut-otlV' ;^^ it is invariably termed 

 in this country) from its connection with the boiler, expands itself 

 as the piston proceeds, until, at the end of the stroke, its tension is 

 but little more than sufficient to overcome the friction of the engine 

 ■svhen it is released ; and after traveling through a " heater " to 

 M-arm a supply of feed water, it floats away into the atmosphere, 

 gradually imparting its remaining heat thei'eto, and being itself 

 absorbed thereby. If the round of operations is properly performed 

 in the the manner here indicated, it is the most economical use 

 nornuilly made of heat in connection with non-condeusing engines; 

 but the proportion which is thrown out to serve the ignoble end of 

 warming the external atmosphere, ranged in the engines in question 

 between eighty-nine and ninety -nine i)er cent, even of the fraction 

 which had been nnmufactured into steam. The calculations in the 

 last two columns in the table are based on the approximately correct 

 supposition that each pound of steam contains, including both sensible 

 and latent heat, 1,'212 degrees Fahrenheit above- zero, or about 1,000 

 units above the ordinary boiling point ; and that the absolute mechani- 

 cal equivalent of a unit of heat, or sufficient to warm one pound of 

 water one degree Fahrenheit, is the elevation of 77:^ pounds, one foot. 



