larger percentage of the day, until finally a load is reached which he
can carry in his hands all day long without being tired out. When that
point has been arrived at this law ceases to be useful as a guide to a
laborer's endurance, and some other law must be found which indicates
the man's capacity for work.

When a laborer is carrying a piece of pig iron weighing 92 pounds in his
hands, it tires him about as much to stand still under the load as it
does to walk with it, since his arm muscles are under the same severe
tension whether he is moving or not. A man, however, who stands still
under a load is exerting no horse-power whatever, and this accounts for
the fact that no constant relation could be traced in various kinds of
heavy laboring work between the foot-pounds of energy exerted and the
tiring effect of the work on the man. It will also be clear that in all
work of this kind it is necessary for the arms of the workman to be
completely free from load (that is, for the workman to rest) at frequent
intervals. Throughout the time that the man is under a heavy load the
tissues of his arm muscles are in process of degeneration, and frequent
periods of rest are required in order that the blood may have a chance
to restore these tissues to their normal condition.

To return now to our pig-iron handlers at the Bethlehem Steel Company.
If Schmidt had been allowed to attack the pile of 47 tons of pig iron
without the guidance or direction of a man who understood the art, or
science, of handling pig iron, in his desire to earn his high wages he
would probably have tired himself out by 11 or 12 o'clock in the day. He
would have kept so steadily at work that his muscles would not have had
the proper periods of rest absolutely needed for recuperation, and he
would have been completely exhausted early in the day. By having a man,
however, who understood this law, stand over him and direct his work,