So long as timber was used for the construction of ships, the number of vessels built annually, especially in so small an island as Britain, must necessarily have continued very limited. Indeed, so little had the cultivation of oak in Great Britain been attended to, that all the royal forests could not have supplied sufficient timber to build one line-of-battle ship annually; while for the mercantile marine, the world had to be ransacked for wood, often of a very inferior quality. Take, for instance, the seventy-eight gun ship, the Hindostan, launched a few years ago. It would have required 4200 loads of timber to build a ship of that description, and the growth of the timber would have occupied seventy acres of ground during eighty years.[2] It would have needed something like 800,000 acres of land on which to grow the timber for the ships annually built in this country for commercial purposes. And timber ships are by no means lasting. The average durability of ships of war employed in active service, has been calculated to be about thirteen years, even when built of British oak. Indeed, years ago, the building of shipping in this country was much hindered by the want of materials. The trade was being rapidly transferred to Canada and the United States. Some years since, an American captain said to an Englishman, Captain Hall, when in China, "You will soon have to come to our country for your ships: your little island cannot grow wood enough for a large marine." "Oh!" said the Englishman, "we can build ships of iron!" "Iron?" replied the American in surprise, "why, iron sinks; only wood can float!" "Well! you will find I am right." The prophecy was correct. The Englishman in question has now a fleet of splendid iron steamers at sea. The use of iron in shipbuilding had small beginnings, like everything else. The established prejudice--that iron must necessarily sink in water--long continued to prevail against its employment. The first iron vessel was built and launched about a hundred years since by John Wilkinson, of Bradley Forge, in Staffordshire. In a letter of his, dated the 14th July, 1787, the original of which we have seen, he writes: "Yesterday week my iron boat was launched. It answers all my expectations, and has convinced the unbelievers, who were 999 in 1000. It will be only a nine days' wonder, and afterwards a Columbus's egg." It was, however, more than a nine days' wonder; for wood long continued to be thought the only material capable of floating.