The other great revolution was the introduction of iron instead of wood as the material for constructing ships. The history of that achievement forms part of the subject-matter of Part II. During the first half of the nineteenth century, good English oak had been becoming scarcer and more expensive. Shortly after the Restoration the price paid for native-grown oak was about L2 15_s._ a load, this being double its value in the reign of James I. The great consumption at the end of the eighteenth and the beginning of the last century had so diminished the supply, that in 1815, the year in which the great Napoleonic wars terminated, the price had risen to L7 7_s._ a load, which was, probably, the highest figure ever reached. In 1833 it sank to L6, and then continued to rise till, in 1850, it had reached L6 18_s._ per load. In consequence of the scarcity of English oak many foreign timbers, such as Dantzic and Italian oak, Italian larch, fir, pitch pine, teak, and African timbers were tried with varying success. In America timber was abundant and cheap, and this was one of the causes which led to the extraordinary development of American shipping in the first half of the nineteenth century, and it is probable that, but for the introduction of iron, which was produced abundantly and cheaply in this country, the carrying trade of the world would have passed definitely into the hands of the people of the United States. The use of iron and steel as the materials for construction have enabled sailing ships to be built in modern times of dimensions which could not have been thought of in the olden days. These large vessels are chiefly employed in carrying wheat and nitrate of soda from the west coast of South America. Their structural arrangements do not differ greatly from those of iron and steel steamers which are described in Part II. APPENDIX. DESCRIPTION OF A GREEK BIREME OF ABOUT 800 B.C.