When the proportion of the power to the tonnage remains unaltered, the speed of the vessel does not materially change. We may therefore assume that 10 pounds of coal per horse power will carry a sea-going steamer adapted for long voyages 7-1/4 miles direct distance; and therefore to carry her 100 miles will require 138 pounds, or the 1/16th part of a ton nearly. Now, the Mediterranean steamers are capable of taking a quantity of fuel at the rate of 1-1/4 tons per horse power; but the proportion of their power to their tonnage is greater than that which would probably be adapted for longer runs. We shall, therefore, perhaps be warranted in assuming that it is practicable to construct a steamer capable of taking 1-1/2 tons of fuel per horse-power. At the rate of consumption just mentioned, this would be sufficient to carry her 2400 miles in average weather; but as an allowance of fuel must always be made for emergencies, we cannot suppose it possible for her to encounter this extreme run. Allowing, then, spare fuel to the extent of a quarter of a ton per horse-power, we should have as an extreme limit of a steamer's practicable voyage, without receiving a relay of coals, a run of about 2000 miles. (120.) This computation is founded upon results obtained from the use chiefly of the North of England coal. It has, however, been stated in evidence before the select committee above mentioned, that the _Llangennech_ coal of Wales is considerably more powerful. Captain Wilson, who commanded the HUGH LINDSAY steamer in India, has stated that this coal is more powerful than Newcastle, in the proportion of 9 to 6-1/2.[43] Some of the commanders of the Mediterranean packets have likewise stated that the strength of this coal is greater than that of Newcastle in the proportion of 16 to 11.[44] So far then as relates to this coal, the above estimate must be modified, by reducing the consumption nearly in the proportion of 3 to 2. [Footnote 43: Vide Report of Select Committee on Steam Navigation, p. 152.] [Footnote 44: Ibid. p. 7.] The class of vessels best fitted for undertaking long voyages, without relays of coal, would be one from about 800 to 1000 tons measurement furnished with engines from 200 to 250 horse-power.[45] Such vessels could take a supply of from 300 to 400 tons of coals, which being consumed at the rate of from 20 to 25 tons per day, would last about fifteen days. [Footnote 45: Engines in steam vessels generally work considerably above their nominal power. The power, however, to which we uniformly refer is the nominal power, or that power at which they would work with steam of the ordinary pressure.]