d
waterways are stronger than the purposes of men. That freights are
regulated by "what the traffic will bear" is merely another way of saying
that transportation comes under the universal law of values--what the
service is worth in the market, or what people are willing to give for it.
According to good authority, the net profit of carrying one ton of freight
one mile has fallen in twenty-five years from one cent to less than
one-ninth of a cent. The same principle fixes a classification of freight
according to service. We can afford to pay more for carrying valuable
produce than for carrying cheaper products. It also leads to special rates
for developing traffic, as illustrated in rates on baled alfalfa hay from
western plains to Chicago.

Wise managers, if not misled by speculation in stocks, care more for
enlarging traffic than for immediate returns upon a smaller bulk, because
the bulk of profit is greater. A good illustration of development of a
special traffic is found in the milk trains running two hundred or three
hundred miles to supply the city of New York. The railroads are compelled
by the needs of the traffic to carry the milk cheaply enough to prevent
its being made into butter and cheese. Laws regulating this charge are
effective, because such a necessity exists in the nature of the case.

_Weights and measures._--Another important growth in the machinery of trade
is found in standards of quantity,--weights and measures of every kind. It
is scarcely possible to realize the uncertainty of exchange without exact
weights and measures. The story of the Indian trader who bought furs by
weight, putting his hand upon the scales for one weight and his foot for
its double, illustrates how uncertain such judgments of quantity may be
without system. The present names of weights and measures indicate their
origin in similar ways.

Measures have usually been connected with some part of the body: as
"finger," used one way in measuring the load of a gun and another on a
stocking; "hand," still used in measuring the height of horses; "span,"
once considered sufficiently definite for any measurement; "foot," now
made to conform to an accurate system; and "pace," still used in many
communities. Connected with the arm, are "cubit" and "yard." Many ladies
still measure their dress goods by arm's lengths. For small measures,
"grain" and "barley-corn," still used as names, indicate dependence upon
average quantity in articl