[155] In an address by Mr. Lothian Bell (May 1875), late President of the Iron and Steel Institute of Great Britain, the area of pit coal in the United States is computed at 192,000 square miles, as compared with 8000 square miles in the United Kingdom. Hitherto the expense of working any portion of these vast coal fields was too great to make it remunerative, but, now, the use of coals is being so rapidly substituted for wood in the American steamers that the facilities for working the mines and transporting the coals has marvellously increased within the last twenty years. Mr. Bell remarks, in the same address, that 20,000 tons of coal are sometimes embarked at Pittsburg on a flotilla of flat bottomed boats towed by one steamer and conveyed 1600 miles down the Ohio at something under a shilling a ton, including the cost of bringing back the empty barges. [156] Between 1816 and 1848 no less than 233 steam-boats employed on American waters exploded, some of them involving terrible disasters, the lowest number during that period being one annually, but sometimes there were as many as ten, twelve, and thirteen in the course of a year. The loss of life in each accident averaged eleven persons, being a total of 2563 human beings killed, besides 2097 persons wounded. In one terrible explosion, that of the _Louisiana_, on the New Orleans _levee_, nearly 200 persons lost their lives. See _St. Louis Republican and Insurance Reporter_ (U.S.A.). [157] In the rule for nominal horse-power, Watt assumed 7 lbs. of steam as a mean pressure. [158] I am enabled through the courtesy of Mr. Webb, the well-known ship-builder of New York, to furnish in the Appendix No. 6, p. 600, a description of the engines of the _Bristol_ and _Providence_, the two finest steamers at present (1875) employed on the line between New York and Boston. [159] Coals are now worked from mines on the coast, and, from this and other causes, the price of coals on the Pacific coast has been materially reduced. [160] These “magnificent” vessels are each 5560 tons burden, and are 423 feet in length, 48 feet wide, and 38 feet deep. They are the largest steam-ships that have ever carried the American flag. It is confidently believed in America, that the running time from Hong Kong to San Francisco, viâ Yokohama, by these vessels will be reduced to within twenty days; and they are guaranteed by the builder, under a heavy penalty, to make fourteen and a half knots per hour. The _City of Pekin_, on her trial trip, made fifteen knots an hour, with fifty-three revolutions per minute and 57 lbs. of steam. This company has now in course of construction another three steamers similar in size; all are being built of _iron_ at Chester, Pa., U.S. Each vessel will have capacity for 800 passengers, and 3000 measurement tons of freight.