quare inch.

Ocean steamships have gradually evolved into two types. The freighter,
broad in beam and capacious, is built to carry an enormous amount of
freight at a moderate speed. The White Star liner Celtic is a vessel of
this class; her schedule time between New York and Liverpool is about
nine days. The Philadelphia of the American line, though not the fastest
steamship, makes the same trip in an average time of five and one-half
days.[7]

Twin-screws, instead of a single propeller, are employed on nearly all
the large liners. The gain in speed is not greatly increased, but the
vessel is far more manageable with two screws than with one; moreover,
if one engine breaks down, the vessel can make excellent time with the
other.

Triple-expansion engines are almost universally used on modern
steamships, and a pound of coal now makes about three times as much
steam available as in the engines formerly used. As a result a bushel of
wheat is now carried from Fargo, N. Dak., to Liverpool for about
twenty-one cents--less than one-half the freight tariff of 1876.

[Illustration: THE SCHOONER THOMAS A. LAWSON. THE FIRST SEVEN-MASTED
SAILING-VESSEL]

The fastest liners consume from three hundred and fifty to more than
four hundred tons of coal a day, and for each additional knot of speed
the amount of coal burned must be greatly increased. Freighters like the
Celtic consume scarcely more than half as much as those of the Kaiser
Wilhelm II. type.

=Sailing-Craft.=--In spite of the growth and development of
steam-navigation, a large amount of freight is still carried by
sailing-craft; moreover, it is not unlikely that the relative proportion
of ocean freight carried by sailing-vessels will increase rather than
decrease, especially in the case of imperishable freight.

The square-rigged ship, or bark, has been very largely replaced by the
fore-and-aft, or schooner-rigged vessel. A large full-rigged ship
requires a crew of thirty to thirty-six men; a schooner-rigged vessel
needs from sixteen to twenty. These vessels are commonly built with
three and four masts; some of the largest have six or seven. They carry
as many as five thousand tons of freight at a speed of about ten
knots--only a trifle less than that of an ordinary tramp freighter. Some
of the larger vessels are provided with auxiliary engines and propelling
apparatus, which enables them to enter or to leave port without the
assistance of a tug. Donkey-engines hoi