单项选择题
| By the 1820’s in the United States,
when steamboats were common on western waters, these boats were mostly powered
by engines built in the West (Pittsburgh, Cincinnati, or Louisville), and of a
distinctive western design specially suited to western needs. The first steam
engines (21) practical use in England and the United States
were (22) low-pressure design. This was the type first
(23) by James Watt, then manufactured by the firm of Boulton and
Watt. Steam was (24) in a large, double-acting vertical
cylinder, but the steam reached only a few pounds of pressure per square inch.
It was low-pressure engines of this type that (25) first introduced
into the United States by Robert Fulton. He (26) such a Boulton and
Watt engine from England to run the Clermont. But this type of engine was
,expensive and complicated, (27) many precision-fitted moving
parts. The engine that became standard on western steamboats was of a different and (28) design. It was the work primarily of an unsung hero of American industrial progress, Oliver Evans (1755-1819), the (29) son of a Delaware farmer. Evans early became (30) by the possibilities of mechanized production and steam power. As early as 1802 he (31) a stationary steam engine of high-pressure design in his mill. Engines of this type were not (32) , but before Evans they were generally considered (33) and dangerous. Within a decade the high-pressure engine, the new type, had become standard on western waters. Critics (34) of western conditions often attacked it as wasteful and dangerous. But people who really knew the Ohio, the Missouri, and the Mississippi (35) , with good reasons, that it was the only engine for them. In (36) western rivers the weight of vessel and engine (37) important; a heavy engine added to the problem of navigation. The high-pressure engine was (38) lighter in proportion to horsepower, and, with less than half as many moving parts, was much easier and cheaper to repair. The main advantages of low-pressure engines were safe operation and (39) of fuel consumption, (40) of which meant much in the West.. |