constitutes a full day's work for a first-class laborer, and our data
had been so carefully collected and recorded that he felt sure that the
necessary information was included somewhere in the records. The problem
of developing this law from the accumulated facts was therefore handed
over to Mr. Carl G. Barth, who is a better mathematician than any of the
rest of us, and we decided to investigate the problem in a new way, by
graphically representing each element of the work through plotting
curves, which should give us, as it were, a bird's-eye view of every
element. In a comparatively short time Mr. Barth had discovered the law
governing the tiring effect of heavy labor on a first-class man. And it
is so simple in its nature that it is truly remarkable that it should
not have been discovered and clearly understood years before. The law
which was developed is as follows:

The law is confined to that class of work in which the limit of a man's
capacity is reached because he is tired out. It is the law of heavy
laboring, corresponding to the work of the cart horse, rather than that
of the trotter. Practically all such work consists of a heavy pull or a
push on the man's arms, that is, the man's strength is exerted by either
lifting or pushing something which he grasps in his hands. And the law
is that for each given pull or push on the man's arms it is possible for
the workman to be under load for only a definite percentage of the day.
For example, when pig iron is being handled (each pig weighing 92
pounds), a first-class workman can only be under load 43 per cent of the
day. He must be entirely free from load during 57 per cent of the day.
And as the load becomes lighter, the percentage of the day under which
the man can remain under load increases. So that, if the workman is
handling a half-pig, weighing 46 pounds, he can then be under load 58
per cent of the day, and only has to rest during 42 per cent. As the
weight grows lighter the man can remain under load during a larger and