The efficiency of the ship and machinery in fulfilling the various and often conflicting conditions of economical service is a matter with which the naval architect and the marine engineer have jointly to deal. Where the conditions cannot all be equally satisfied, it is the province of these two to make that sort of compromise which gives the best results in each special case. In cargo-carrying vessels, for example, an economy in the consumption of fuel may often be the dominant and regulating quality. An economy of one-fourth of a pound per horse-power per hour gives, on a large transatlantic steamer, a saving of about 100 tons of coal for a single voyage. To this saving of cost is to be added the gain in wages and sustenance of the labour required to handle that coal, and the gain by 100 tons of freight carried in place of the coal. Again, it is estimated that every ton of dead-weight capacity is worth on an average £10 per annum as earning freight. Supposing, therefore, the weight of machinery and water in any ordinary vessel to be 300 tons, and that by careful design and judicious use of materials the engineer can reduce it by 100 tons without increasing the cost of working, he makes the vessel worth £1,000 per annum more to her owners. To these and other such considerations, which often influence the naval architect and engineer in their designs, and due regard to one or more of which not infrequently prevents the attainment of all-round success, should be added many others concerned with the after-management of vessels. For example, the length of voyage to be performed, the seasons and the markets in particular trades, the number of ports of call, and the coaling facilities at each, are all matters which must be taken into consideration when measuring, from one standpoint or from particular instances, the degree of success attained in general. The diminution in coal consumpt, coincident with the increase of steam pressure and the acceleration in speed which has been attained in recent years measures the principal element of progress. In many of the “racers” of recent times, it is true, speed is attained at what may appear a great sacrifice of fuel, but these are cases in which the commercial considerations often used to measure the efficiency of ordinary cargo-carrying steamers are not applicable. Owners—of transatlantic steamships especially—realise from experience that “speed pays,” and they find it of more advantage to ensure certainty of arrival at the port of destination than to save a few tons of coals on the voyage.