As further instances of the effect produced by the same causes,—in 1740, before the establishment of canals, the iron manufactured in England and Scotland employed 59 furnaces, which produced annually 17,000 tons. In 1827 there were upwards of 280 furnaces, with an annual produce of 690,000 tons; during the intervening period canals were cut, connecting the iron districts with large towns and the ports. In 1750 there was but one smelting furnace in Staffordshire, making less than 2,000 tons of iron per annum. In 1827 there were 97 furnaces in that district only, making 216,000 tons per annum. The population of Staffordshire in 1750 was 160,000; it is now upwards of 350,000. In England in 1750 it was 6,017,000; it is now upwards of 13,000,000. The total amount of the exports in 1750 was 7,772,039_l._; in 1824 it was 56,234,663_l._ In 1760 the number of ships assessed in Liverpool was 1,245; in 1824, it was 10,001. These statements are sufficient to show the changes consequent upon the introduction of canals. It was found, that one horse upon a canal could convey twenty times what he could upon a road; and that what formerly cost six pounds to send a hundred miles, could by canals be sent for little more than one pound. Such is the traffic upon the Birmingham Canal alone, that at some periods there is a weight of goods and materials brought by 150 horses and boats, in one day, which by the roads would require 3,000 horses and 1,000 waggons. We find again that the population has more than doubled itself in three principal inland towns, viz. Birmingham, Manchester, and Leeds, since the establishment of canals. But notwithstanding the advantages that have attended upon the introduction of canals, there are limits within which their utility is confined, and, as regards despatch, much confined. The canals as they are now constructed are adapted only to horse power, and are subject to the inconvenience of that slowness of travelling which arises from the great increased resistance of fluids to bodies moving in them, with only a very slight increase of velocity. Two horses may take a loaded boat of twenty-five tons at the rate of four miles per hour; but to obtain a velocity of twelve miles per hour, it would require twenty-seven horses. It is found that with a velocity of six miles per hour so great a surge or swell is produced in the water as to hazard the sinking of any boats that are passing.