HISTORY OF THE STEAM ENGINE. 487 
although an invention usually ascribed to another, were invented by Watt, and 
the condensing apparatus, the expansion gear, the governor, and even that won- 
derful little instrument, the ‘‘indicator’”—the engineer’s stethoscope—all came: 
down to us from the same source. 
Watt learned the leading facts and made the greatest modifications of plan, 
while it was reserved for our contemporaries to contribute the refinements of its. 
design and of its manufacture, and to study the more deeply hidden principles of 
its philosophy, and to determine more definite rules for its construction and man- 
agement. 
Those of you who have been familiar with the design and construction of 
steam engines during the past twenty or thirty years, f and those of you who have 
been for a generation past accustomed to handle this miracle of art will remember, 
as I remember well, how we learned at a very early period in our experience cer- 
tain cardinal points of practice which were very strongly impressed upon us. We 
soon learned by experience that efficiency was gained only as we learned to 
_ handle higher steam with properly adjusted expansion, to work our engines up 
to higher piston speeds, to cushion heavily when we had large clearance, to 
reduce that clearance to a minimum, to adjust the size of our engine to its work, 
and to determine the point of cut-off, under proper conditions otherwise, by the 
governor.{ We learned that the now well-known ‘‘ American Automatic Cut-off 
Engine,” with its high steam and moderately large expansion, as exemplified by 
the ‘‘ Corliss Engine,” which is now built all over the world, was the representa- 
tive of the best general practice. 
But we were not satisfied. Twenty years ago we began to understand that 
we had yet to perfect the phylosophy of the steam engine, and that it was still 
apparently far from perfect efficiency. We then discovered that while our best 
engines were consuming from twenty-five to thirty pounds of dry steam per horse 
power per hour, the mechanical equivalent of the heat supplied in the steam in 
boiler was sufficient to give about a horse power for each two pounds of high- 
pressure steam per hour, and hence that we were utilizing but one tenth or 
one-fifteenth of the heat we were paying for when we settled our coal bills, 
Next, we found that, owing to the fact that we can not practically expand 
down to a pressure lower than that due approximately to the temperature of 
surrounding bodies, we must therefore discharge heat unutilized, that the lar- 
ger part of this waste is unavoidable and that an engine, perfect mechanically, 
and working within the usually practicable maximum limits, must waste three- 
fourths, and can return useful effect from but one-fourth, of the heat supplied, 
thus placing the practical limit under known conditions at about eight or ten 
pounds of steam per hour and per horse power. 
And here we stand to-day with the steam engine, mechanically almost perfect, 
yet with a theoretical economy of about eight or ten pounds of steam per horse 
+ Reports on Machinery and Manufacturers at Vienna, 1873, by R. H. Thurston, etc., ete., Wash., 1875. 
} History of the Growth of the Steam Engine; International Series; N. Y., 1878, p. 473. 
