这段叙述出处:
http://d29qn7q9z0j1p6.cloudfront.net/content/371/1986/20110568
正在看一篇E. A Wrigley写能源与工业革命的文章，
这边作者引用的文字我一直看不懂，
翻译感觉比较能理解文章，但这串文字不知道是否有理解错误的地方，
希望能请版上大大指点迷津!!! 谢谢~~~~~
我的试译:
A coal miner who consumes in his own body about 3,500 calories a day, will,
if he mines 500 pounds of coal, produce coal with a heat value of 500 times
the heat value of his food which he consumed while mining it.
一名每日消耗3500卡路里热量的煤矿工人，假设他开采500镑的煤炭，其产出的煤炭热值
是开采时所消耗之食物热值的500倍。
At 20 percent efficiency, he expends about 1 horsepower of mechanical energy
to get the coal.
在效率20%的情况下，他开采煤炭所消耗的机械能约1马力。
Now if the coal he mines is burned in a steam engine of even 1 percent
efficiency, it will yield about 27 horsepower-hours of mechanical energy.
现在，如果他开采的煤炭，经效率仅1%的蒸汽机燃烧后，将能产出27马力时（
horsepower-hours）的机械能。
（这里的马力时可以理解成每小时27马力吗？）
The surplus of mechanical energy gained would thus be 26 horsepower-hours, or
the equivalent of 26 man- days per man-day.
扣掉该人一天消耗的机械能后，所剩余的机械能约26马力时，或者相当于26人一天所生产
的能量。
A coal miner who consumed about one-fifth as much food as a horse, could thus
deliver through the steam engine about four times the mechanical energy which
the average horse in Watt’s day was found to deliver.
一个煤矿工人大约可以消耗马的五分之一粮食，透过蒸汽机可以输出的机械功率比平均马
只多出四倍。