To embrace to the utmost advantage these various essential qualities in a merchant-vessel, the trade in which she is to be employed requires to be considered with her mercantile capabilities in relation to cost and speed. These calculations must be carefully gone into so as to obtain an approximate estimate of the commercial advantage with regard to the cost of freight per ton, that attends the employment of ships suitably constructed for the service in which they may be employed as compared with vessels of inferior adaptation. By this investigation, the comparative financial balance of outlay and expenditure and, consequently, the income to be expected from one vessel as compared with another, may be equitably apportioned. Such considerations as these are essential to success, and cannot be neglected by any shipowner who understands his business. They will not only conduce to an effective direction and management of mercantile shipping, and of financial economy, but, also, in case a vessel fails to fulfil an assigned service, the degree in which such failure may be attributable to faults of original construction (producing a low scale of locomotive efficiency), or to defective management or to imperfect navigation, may be determined. Moreover, steamship proprietors, especially, would thus be enabled to ascertain the relative value of their stock, not, indeed, as respects the intrinsic value of the respective ships, but as respects their relative working properties and consequent value for any special service. Each vessel might thus be assigned its most appropriate duty, and ships, manifestly unsuitable for one line of trade, might be otherwise employed or disposed of, instead of being put on services which they are _constructively_ inadequate to perform. For example, a vessel may be well suited for the economical conveyance of cargo at eight miles an hour, but, being employed upon a service demanding a higher rate of speed, and failing to attain this, is held to be inefficient, while the value of the ship becomes unduly depreciated, and incapacity of _direction_, the real cause of the failure, escapes due observation. FOOTNOTES: [96] It would appear from Dr. Robinson’s interesting narrative (Muirhead, “Life of Watt,” p. 65), that Watt’s first connection with the steam-engine arose from his having been desired, by the Professors of Natural Philosophy in the University of Glasgow, to repair a model of one of Newcomen’s engines in the year 1764. (See Smiles’ “Lives,” p. 121.) [97] See Tredgold “On the Steam-engine,” and Woodcroft, p. 82. [98] The following is a copy, from “Memorials of James Watt” by George Williamson, Esq., late perpetual Secretary of the Watt Club of Greenock, printed for the Club, of Mr. Bell’s original advertisement of his new steamer the _Comet_ to ply between Glasgow, Greenock, and Helensburgh:— STEAM PASSAGE BOAT, THE ‘COMET,’ between Glasgow, Greenock, and Helensburgh, for passengers only.