cean traffic. For a similar reason, river and canal freights
are higher than lake freights. Railway transportation is economical,
partly because a single locomotive will draw an enormous weight of
goods, and partly because of the high speed at which the goods move from
point to point. Animal transportation is more expensive than any other
means ordinarily employed.

=Ocean Transportation.=--In many respects, water-routes form the most
available and economical methods of transportation. Intercontinental
commerce must be carried on by means of deep-water vessels. Therefore an
extraordinary development of ocean carriers has taken place in the past
century.

One important period of development began with the rise of American
commerce. Just after the close of the War for Independence, it was found
that deep-water ships could be built of New England timber for
thirty-five dollars per ton, rated tonnage, while a vessel of the same
burden built in Europe cost about forty-five dollars per unit of
tonnage. Two types of vessels came into use--one, the clipper ship with
square sails, was used for long ocean voyages; the other, the schooner,
with fore-and-aft rigging, was employed mainly in the coast-trade.

[Illustration: A SQUARE-RIGGED SHIP--A TYPE NOW BEING REPLACED BY
FORE-AND-AFT RIGGED SCHOONERS]

In speed and ease of management these vessels surpassed anything that
had ever sailed. In time they became the standards for the
sailing-vessels of all the great commercial nations. The types of the
vessels are still standards.

[Illustration: THE DEVELOPMENT OF THE MODERN STEAMSHIP]

=The Development of the Steamship.=--Another important era in ocean
commerce began when steam was used as a motive power for vessels. The
first deep-water vessel thus to be propelled was the Savannah. Her
steam-power was merely incidental, however, and her paddle-wheels were
unshipped and taken aboard when there was enough wind for sailing. Up
to 1860 almost all the ocean steamships were side-wheelers, propelled by
low-pressure beam-engines.

The next most important improvement was the screw-blade propeller,
placed astern. This means of propulsion called for higher speed of the
engines, and in a very short time compactly built high-pressure engines
took the place of the low-pressure engine with its heavy walking-beam.
The latter carried steam at a pressure varying from twenty to thirty-two
pounds; the modern boiler has steam at 260 pounds per s