and rather less than 2,300 tons of cargo, stores, etc., on board. If a steamship of similar dimensions were required to do the voyage at 15 knots, her design would have to be such that the displacement would not be more than 4,100 tons, the I. H.-P. at least 3,400, and the amount of fuel stored at the commencement of the voyage 1,618 tons. The machinery would probably have to be at least 400 tons heavier, so that the capacity for cargo, stores, etc., would now be reduced to 1,000 tons. The cost, too, would be greatly increased on account of the extra engine-power, and the expense in fuel would be more than doubled. The engine-and boiler-room staff would likewise be materially increased, while the earning power of the vessel would be less than half. Seeing, however, that the power required for a certain speed varies with the cube root of the displacement squared, the proportion of power to tonnage will decrease considerably with the increase in the size, so that if, instead of the steamer above referred to of 4,100 tons, one were taken of 8,200 tons, the I. H.-P. for 15 knots—all other things remaining the same—would be very little more than 5,000; _i. e._, with a ship of twice the size the increase of engine-power is only forty-seven per cent. The carrying capacity and consequent earning power of such a boat is immeasurably more than that of the small one. The larger ship will, moreover, make better passages, and generally be much more economical in working, as the officers and crew will not very largely exceed that of the smaller vessel. * * * * * It was, however, owing to the more economical engine that advances in speed were rendered possible, and this is seen by referring back to the original ship, and supposing that instead of engines burning 4 pounds of coal per I. H.-P., it had ones consuming only 2-1/2 pounds per I. H.-P. in which case the expenditure on the voyage would be reduced from 1,618 tons to 1,004 tons; so that 600 tons more cargo could be taken and the cost of 600 tons of fuel per voyage saved. This was actually the case on the substitution of compound for old-fashioned low-pressure jet-injection engines fitted to the Cunard Company’s steamers as late as 1862, when their largest, fastest, and most improved steamer, the Scotia, was put on the service. But it was not until many years after the advent of the Scotia that such economic engines were in general use on the Atlantic, and it was only in 1874-75, when the Inman Company and White Star Company placed steamships having these engines in competition with the old-fashioned ones, that the day of the latter was gone. [Illustration: Passenger Steamer Princesse Henriette at Full Speed—24-1/2 miles per hour. (Built by William Denny & Co., Dumbarton.)]