It has already been remarked that the consumption of coal, which enters as a most important factor into the question of high speed, both from the weight and cost, had been reduced, by the introduction of the compound engine, from 4 pounds to 2-1/2 pounds per I. H.-P., and latterly, as that engine was improved and higher pressures used, the consumption was further reduced to 2 pounds, and in some cases as low as 1-3/4 pound per I. H.-P. The triple expansion engine, developed within the past eight years, and later the quadruple expansion, have effected a still further saving, until with them and such other means as are now employed, the consumption is under 1-1/2 pound of coal per I. H.-P. The success of the locomotive was very questionable until the exhaust steam was turned into the chimney so as to create a rapid draught, and the steam-blast to-day enables the locomotive to travel at its great speed by causing the comparatively small boiler to generate such a large amount of steam. When this form of boiler was tried on board ship its power would have been very much crippled had not some other means been adopted for forcing the draught, as the steam could not in this case be allowed to escape through the funnel, but must be condensed into water for the use of the boiler. By closing the stoke-hole and forcing into it by mechanical means a plentiful supply of air, this boiler was made to be as efficient for a torpedo boat as for a locomotive. This forced draught has now been adopted on large ships, and to-day the very high speed of naval vessels, and of many mercantile steamers, is due to it. Consequently, with the same weight of machinery, higher powers are developed with a corresponding increase in speed, and the cruiser Piemonte, constructed by Sir William Armstrong & Co., of which an illustration is shown on p. 91, had her speed increased by means of forced draught from 20 knots to 22.3 knots, at which speed she was going when the picture was taken. Mr. James Howden patented a forced draught process by which the incoming air is warmed by the heat (which would otherwise be wasted) in the uptakes and funnels, and then conducted direct to the furnaces; and he claims by this to be able to do with still smaller boilers, besides avoiding the danger to the tubes now sometimes experienced in war ships with closed stoke-holes. [Illustration: Italian Cruiser Piemonte at Full Speed—22.3 knots=25-3/4 miles per hour.]