[Illustration: FIG. 117.--A farm engine putting in a crop.]
168. The Power or the Speed with which Work is Done. A man can load
a wagon more quickly than a growing boy. The work done by the one is
equal to the work done by the other, but the man is more powerful,
because the time required for a given task is very important. An
engine which hoists a 50-pound weight in 1 second is much more
powerful than a man who requires 50 seconds for the same task; hence
in estimating the value of a working agent, whether animal or
mechanical, we must consider not only the work done, but the speed
with which it is done.
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