All the facts yet known with regard to the superior durability[121] of iron ships are highly satisfactory. It is a consideration not to be overlooked that large ships may be rendered more durable than small vessels; for, as the weight of the hull is generally determined in a certain proportion to the whole displacement, and the plates of iron are much thicker in a large than in a small ship (the oxidizing causing an uniform waste of metal), the durability will be in proportion to the amount of wear the plates of the respective vessels can bear without danger to the ship.

But the superior strength of iron ships depends not merely upon the quality of the material employed, but also on the mode of combining it. The strength of wrought iron is well known and its power of resisting strains in almost every direction is a matter of universal experience, add to which, that its resistance to lateral pressure increases in a much higher ratio than the quantity of material. Hence, almost any amount of strength may be given to a large fabric; certainly, enough to bear the pressures and strains to which ships are exposed, with much less liability to injury than wood. With plates of iron of a substance fitly proportioned to the magnitude of the fabric, and with joints properly formed, the sides of ships have been found capable of resisting, in a remarkable manner, forces for which the strength of timber would be quite insufficient. A substance of plates sufficient to constitute this amount of strength generally, is also able to bear concussions of great force with much less hazard than timber. The uninjured state in which the Great Britain was found in Dundrum Bay, after being wrecked and lying on the beach several months during winter, exposed to various storms, proved the correctness of these views, which more extended experience has since confirmed. Experience has also demonstrated that unless the concussion takes place with extreme violence, mere indentation of the metal is generally the greatest injury sustained. Beyond this, the strain sometimes breaks off the heads of a few rivets without opening the seam, but it is uncommon for the rivets to be drawn if the metal and workmanship are good. In the case where an iron ship strikes upon a sharp pointed-like crag of rock or coral reef with considerable force, it frequently happens that a hole is made through the plate; but even when such an accident occurs the damage is generally local, the parts not immediately subject to the concussion remaining unhurt. No general leakage is, therefore, consequent on such an accident, as would be the case in all vessels built of wood.

As the hull of an iron ship is both thinner and considerably lighter[122] than that of a wooden ship, an iron ship of the same external dimensions as a wooden one has both greater capacity for stowage and greater power to support the weights which may be put into her. These differences vary in some degree with the dimensions and form of the ship, being greater in proportion to the increased dimensions of the ship. They may, of course, be determined by computation; but, in all cases, an iron ship will carry considerably more cargo than a wooden one of the same external dimensions.

Again, the consideration of economy must not be omitted in any comparison of the merits of ships built entirely either of timber, or of iron. The economy begins with the construction, for the original cost of an iron ship is less than that of a wooden one, and, apart altogether from her superior capacity for cargo, it runs on with the course of the ship’s service as the result of several causes; as, for instance, the smaller amount and less expensive character of repairs: moreover, as it is not even yet known how long iron ships will last, the precise saving from their use cannot be estimated. On the other hand, the period of service of mercantile timber-built ships is defined. If they reach or exceed thirty years’ service, they must be ships of the very highest class as to quality[123], and must, indeed, within that period have undergone frequent and very expensive repairs. As iron ships are not subject to the same decay, at the same time that accidental damages are generally repaired at a much less cost, every item saved by the diminished charge for repairs is clear profit.

But with all these advantages, a considerable time elapsed before the Admiralty could be induced to consider the desirability of constructing any Government steamer of iron, or of even allowing the large private trading vessels engaged in the conveyance of the mails to be built of that material. They had objections of their own applying specially to the ships under their control, and very plausible objections too, in their opinion, compared with those originally raised by an ignorant public. A shot, they said, would penetrate an iron vessel with much greater ease than a wooden one, while the shot holes could not be as effectually plugged, if indeed they could be plugged at all. Wood, they argued, when pierced, would rapidly contract and leave a very small opening for water to get through, whereas a shot would make a clean cut through an iron plate which could not be thus expeditiously filled, and if it did not tear away the whole of the plate, would leave a gap as large as a “barn door.” However, a little experience[124] soon showed their arguments to be fallacious, and when they found that the engines of a paddle-wheel steamer, and, especially, the paddles themselves, offered conspicuous targets to an enemy, and that it was impossible to make the stern-frames of their wooden ships sufficiently strong to withstand, without serious leakage, the vibration of the screw, they abandoned, though reluctantly, the paddle-wheel, and at length gave up, also, vessels of wood for the purposes of war. These resolutions were, however, only carried into practice after vast sums of money had been expended on the “reconstruction” of a wooden British Navy, for which, in one year alone, and that so lately as 1861, when almost everybody except themselves saw that iron must supersede timber, they demanded from Parliament (and carried their vote) no less than 949,371l. to replenish the stock of wood in the dockyards: a sum far in excess of any previous vote for that material.[125]

While the art of steam navigation made rapid progress, the ingenuity of engineers had been constantly directed to the improvement of the paddle-wheels; and the above drawing of one, with “feathering paddles,” patented by Mr. Galloway in 1829,[126] represents the most perfect of any wheel in use at that period, and has not been materially improved on since then. But, at that time also, a substitute for the paddle was seeking practical solution. The screw, as a means of propulsion, had been suggested long before the steamboat had been brought into use. Indeed, its principle was known at a very early period in the use of an oar for sculling, and could, as already explained, be seen in the movements of the tail of a fish.

Though my faith in the reports of the genius and early inventions of the Chinese has frequently been rudely shaken in the course of my investigation of their reputed discoveries, I may remark that Mr. MacGregor, for whose opinions I entertain no ordinary respect, states, in the paper he read to the Society of Arts,[127] that “the use of the screw-propeller may be of an indefinite antiquity,” and adds that “a model of one was brought from China in 1680, which had two sets of blades, turning in opposite directions.” It was not, however, until 1729, that we have any authentic account of a plan of propulsion, in any way approaching the valuable invention now so largely in use. In that year an ingenious Frenchman, M. Du Quet, described a contrivance by which a screw turned by the water in a stream, wound up a rope for towing vessels, of which the annexed (p. 101) is an illustration.[128] In 1745, Masson describes an apparatus for working an oar at the stern of a vessel so as to give it a “sculling” motion; in 1746 Bougner mentions that “revolving arms, like the vanes of a windmill,” were tried for the propulsion of vessels, and, in 1770, as already incidentally noticed, the celebrated Watt speaks of using a screw-propeller, of which the annexed is a sketch, to be turned by a steam-engine.[129]

In 1779, Matthew Wasborough, to whose genius we are indebted for many inventions in connection with marine propulsion, patented a “new invented machine or piece of mechanism which, when applied to a steam-engine or any reciprocal movement, produces a circular or rotative motion without the medium of a water-wheel;” Joseph Bramah, of whose invention I have already spoken in detail, speaks of (1785) a wheel with inclined fans or wings, similar to the fly of a smoke-jack, which may be turned round either way under water, causing the ship to be forced backward or forward,[130] and, in 1798, he tested the application of a screw in a boat, of which the annexed, copied from Mr. MacGregor’s instructive paper, is an illustration.

In 1800, Edward Shorter patented an invention which he called “a perpetual sculling machine,” having the action of a two-bladed propeller, and which, two years afterwards, was experimented upon in H.M. Ships Dragon and Superb.[131] Various other experiments followed. But, in May 1804, Mr. J. Stevens, of the United States, put to sea with a steam-boat propelled by a screw, turned first by a rotatory engine, and then by Watt’s reciprocating engine; and, as this small craft steamed from Hoboken to New York, she has by some writers been considered the first sea-going screw of which there is any certain account. Richard Trevethick, in 1815, patented “a worm or screw revolving in a cylinder at the head, sides, or stern of a vessel,” as also a “stuffing-box, inclosing a ring of water.”[132] In the following year Robert Kinder applied for a patent for a shaft and screw (almost on the exact plan now in use) with “a shoulder formed upon it so as to work in a water-tight manner through a stuffing-box of the common or well-known form, which stuffing-box and shaft are made to pass through the end of the vessel, just above its ordinary water-line, and is thereby affixed to it.” (See “Specifications of Marine Propulsion,” Part I. p. 64.)

Many other proposals for propelling vessels by means of the screw were subsequently made and most of them were patented.[133] Two were tried on a small scale in France by Captain Delisle, a Frenchman, in 1823, and by a countryman of his, M. Frédéric Sauvage, in 1832.[134] In 1833, Mr. Robert Wilson, a Scotchman, afterwards manager of the firm of Nasmyth and Co., at Patricroft near Manchester, brought under the notice of the British Admiralty the screw “perfect in all its details” as a means of propulsion, which he says he invented in 1827, and which he states[135] the officers of the Woolwich Dockyard, in their official report, rejected because “it involved a greater loss of power than the common mode of applying the wheels to the side.” No great efforts, however, seem to have been made to bring the screw into practical use until 1836, when Captain John Ericsson, C.E. (a native of Sweden, who had established himself in London in partnership with the Messrs. Braithwaites), fully demonstrated its merits according to a plan which he patented on the 13th of July of that year,[136] and carried out successfully.

Instead, however, of launching to the public gaze a vessel on a large scale fitted with his plans, he made a model boat of about 20 inches in length, into which he placed a small engine, and floated her in a large bath over which a steam boiler had been fitted for the supply of hot water. From this boiler a pipe projected to within a foot of the water, where it was branched off by a swivel joint and connected with the engine in the boat. The steam when admitted put the engine in motion, and also the propeller, which at once sent the boat forward with considerable rapidity.

Finding that his invention was likely to succeed when put into practical operation on a larger scale, Ericsson’s next step was to order Mr. Gulliver, a boat-builder at Wapping, to construct for him a boat of wood which he named the Francis B. Ogden. She was 45 feet long and 8 feet wide, drawing 2 feet 3 inches of water. In this vessel he fitted his engine and two propellers, each of 5 feet 3 inches diameter. The result of her first trial went far beyond his most sanguine expectations. No sooner were the engines put at full speed, than she shot ahead at the rate of more than 10 miles an hour, and maintained that speed without a single alteration requiring to be made in her machinery;[137] nor were her capabilities as a tug less surprising. This miniature steamer, tested first by a schooner of 140 tons burden, towed her at the rate of 7 miles an hour during slack water on the Thames; and afterwards by the large American packet-ship Toronto, moving on with her astern at a speed of more than 5 miles an hour. The next experiment was made in the presence of the Lords of the Admiralty, who, accompanied by Sir William Symonds, Sir Edward Parry, and Captain Beaufort, had embarked in their barge to witness the novelty, and judge for themselves as to its efficiency and practical value. They were minute in their inspection, and as they did not, and in fact could not, offer any valid objections to his invention, Captain Ericsson felt confident that they would soon order the construction of a war-steamer on the new principle. In this, however, he was disappointed, though he had given them a very practical proof of its value by towing them in their barge at the rate of 10 miles an hour for a considerable distance—a speed which must have astonished their Lordships. The unseen and comparatively noiseless propeller, although it had furnished the most convincing proofs of its power, failed to propitiate their favour. Scientific theorists had informed the Board that the invention was constructed upon erroneous principles, and full of practical defects (one being that a ship thus propelled would be unsteerable), while engineers as a body regarded its failure as an event so certain as to preclude any speculations of its success. In a word, when publicly discussed, the general opinion was that the vast loss of mechanical power would prevent it from being employed as a substitute for the now old-fashioned paddle-wheel![138]

While Ericsson was making his experiments in the Francis B. Ogden, Mr. Thomas Pettit Smith, who, on the 31st of May, 1836, had taken out a patent for a “sort of screw or ‘worm,’ made to revolve rapidly under water in a recess or open space formed in that part of the after part of the vessel commonly called the dead rising or dead wood of the stern,”[139] was also at work with his invention, and, in the following year, put it into practical operation. His first trial, made in a small vessel of 6 tons burden, with an engine the cylinder of which was 6 inches diameter and 15 inches stroke, was considered by a few far-seeing persons so satisfactory,[140] that they applied for, and obtained on the 29th of July, 1839, an Act of Parliament for incorporating a company called the Steam Ship Propeller Company, to enable them to purchase “certain letters patent,” that is, the screw-propeller of T. P. Smith.

The first successful application of this screw-propeller, on a large scale, was to a vessel called the Archimedes, constructed under the direction of the patentee of the screw, Mr. Smith. Her burden was 237 tons, and her mean draught of water 9 feet 4 inches; the diameter of the cylinder 37 inches, and the length of the stroke of the piston 3 feet; her screw-propeller consisted of two half threads of an 8 feet pitch, 5 feet 9 inches in diameter; each was 4 feet in length, and they were placed diametrically opposite to each other, at an angle of about 45 degrees on the propeller shaft. The propeller itself passed through a hole cut in the dead wood, immediately before the rudder; the keel being continued under the screw. The performance of the engines averaged twenty-six strokes per minute, the revolutions of the screw at the same time being 138⅖. The calculations of the inventor were that, provided there was no slip or recession, the vessel ought to advance 8 feet for every revolution of the screw, or 12·60 miles per hour. But the utmost speed ever obtained by the Archimedes, under the power of steam alone, was 9·25 nautical miles per hour, showing a loss by recession of rather less than one-sixth under the most favourable circumstances. The Archimedes was not, however, a fair illustration of the screw-propelling principle, as her steam-power was not great enough to drive a screw sufficient for the size of the vessel. Nevertheless, in her subsequent trials from Dover to Calais against the Widgeon, the fastest paddle-steamer on the station, the superior value of the screw-propeller was proved. Although in the first three or four experiments the Widgeon had the advantage by a few minutes, in the subsequent trials, both vessels having set the whole of their sails, the Archimedes, carrying much more canvas than the Widgeon, on a run of 26 miles from Dover to Calais, close hauled, accomplished this distance in nine minutes less time than the Widgeon. Upon the return voyage to Dover, with a fresh breeze abeam and all sail set, the Archimedes, with a speed of ten knots per hour, performed the distance in five and a half minutes less time than the Widgeon.

These experiments decided the practical value of the screw. They proved that the Archimedes was slightly inferior to the Widgeon in light airs, in calms, and in smooth water; but, as the steam power of the former was ten horses less, and her burthen 75 tons more than that of the Widgeon, it is evident that in such vessels the propelling power of the screw alone was equal, if not superior, to the ordinary paddle-wheel. In this respect, therefore, Mr. T. P. Smith’s invention might be considered completely successful. It was evident from the second trial that, in steaming against even a light wind, the low masts and snug rig of the Widgeon gave her an advantage over the Archimedes with loftier masts and heavier rig; but, on the last two trials, the power of the sails operated favourably for the Archimedes, as she then beat the Widgeon, and made the passage between Dover and Calais in less time than it had ever previously been performed by any of Her Majesty’s mail packets. On this occasion the Archimedes went from Dover to Calais in two hours and one minute, and returned in one hour and fifty-three and a half minutes.[141]

Although the successful performances of the Archimedes brought the screw into more general notice, it does not appear that she was ever employed as a trading vessel. After several experiments she lay for a long time in the East India Dock advertised for sale, and her spirited proprietors, who had been so instrumental in promoting the introduction of the screw-propeller, lost all the capital they had invested in this important undertaking.

As the Widgeon and Archimedes differed materially in size and form, an exact comparison could not be made by them between the performance of the screw and that of the paddle; but the result of these trials nevertheless showed (especially when the peculiar fitness of the screw for war purposes was taken into consideration) the propriety of having a further and fairer trial of this novel instrument. With this object in view the Rattler was ordered to be built,[142] and, that the experiment might be conclusive so far as a trial could be made between two vessels, she was constructed on the same lines as the Alecto (her after part being lengthened for the insertion of the screw), and fitted with engines of the same power, and on a plan which had been previously tried with paddle-wheel vessels.

The river trials of the Rattler lasted from October 1843 to the beginning of 1845, and showed that the screw-shaft might be advantageously reduced in diameter, and the blades by about one-third of their length, an alteration which greatly reduced the weight of the screw, and facilitated the operation of shipping and unshipping it, while rendering unnecessary the wounding to so great an extent of the after part of the vessel. Before, however, this last point was decided (it not being evident that the good performance of the shorter screw was not attributable to the greater clearance which the reduction of its length had caused), the screw aperture was partly filled up in a temporary manner, so as to leave the shorter screw the same clearance as the longer one had originally. The result of this experiment proved that the aperture in future vessels might be constructed of very moderate dimensions without lessening the propelling power of the screw.

These trials clearly showed that the screw, as an instrument of propulsion in smooth water, is not inferior to the paddle-wheel. But further experiments were considered necessary to establish its superiority in all respects. In the early part of the year 1845 the Rattler proceeded, in company with the Victoria and Albert and the Black Eagle, from Portsmouth to Pembroke. When rounding the Land’s End, and steaming against a strong head wind, both these vessels, as might be expected, showed a great superiority, their power being much greater than the Rattler’s in proportion to the resistance, and their paddle-floats being constructed on the feathering principle. This comparative failure of the Rattler left an unfavourable impression as to the efficiency of the screw against wind and sea in heavy weather, and this impression continued for several years, although when next tried in a run from the Thames to Leith, she showed in respect to speed a decided superiority over one of the paddle-wheel vessels employed in that trade, whose power as compared with her tonnage was greater than that of her competitor. Before joining the squadron under the command of Rear-Admiral Hyde Parker in July 1845, the Rattler was employed to tow the Erebus and Terror to the Orkney Islands on their fatal expedition to the North Pole, and she seems to have performed that duty to the entire satisfaction of Sir John Franklin.

In following the progress of the screw as applicable to the propulsion of merchant vessels, and its use in other countries, I must now recur to the period when Ericsson was making his experiments on the Thames. At that time an intelligent gentleman, Captain Robert F. Stockton, of the United States Navy, was on a visit to London. Being of an inquisitive turn of mind, like most of his countrymen, and fond of scientific pursuits, he watched with great interest the trials with the screw then in progress, and having obtained an introduction to Ericsson, he accompanied him on one of his experimental expeditions on the Thames. Unlike the Lords of the British Admiralty, who allowed eight years to elapse before they built their first screw-propeller, the Rattler, Captain Stockton was so strongly impressed with the value and utility of the discovery, that, though he had made only a single trip in the Francis B. Ogden, and that merely from London Bridge to Greenwich, he there and then gave Ericsson a commission to build for him two boats for the United States, with steam machinery and propeller as proposed by him. Stockton, impressed with its practical utility for war purposes, was undismayed by the recorded opinions of scientific men, and formed his own judgment from what he himself witnessed. He, therefore, not only ordered the two iron boats on his own account, but at once brought the subject before the Government of the United States, and caused various plans and models to be made at his own expense, explaining the peculiar fitness of the new invention for ships of war. So sanguine was he, indeed, of the great importance of this new mode of propulsion, and so determined that his views should be carried out, that he encouraged Ericsson to believe that the Government of the United States would test the propeller on a large scale; Ericsson, relying upon these promises, abandoned his professional engagements in England, and took his departure for the United States. But it was not until a change in the Federal administration, two years afterwards, that Captain Stockton was able to obtain a favourable hearing. Orders were then given to make the experiment in the Princeton, which was successful. The propeller, as applied to this war-vessel, was similar in construction to that of the Francis B. Ogden, as well in theory as in minute practical details.

One of these boats, named, after her owner, the Robert F. Stockton, was built of iron by Messrs. Laird of Birkenhead, and launched in 1838. She was 70 feet in length, 10 feet wide, and drew 6 feet 9 inches of water. Her cylinders were 16 inches diameter with 18 inches stroke, and her propeller 6 feet 4 inches in length. On her trial trips on the Thames, made in January of the following year, she accomplished a distance of 9 miles (over the land) in 35 minutes with the tide, thereby proving the speed through the water to be between 11 and 12 miles an hour. On her second trial, between Southwark and Waterloo bridges, she took in tow four laden barges, with upright sides and square ends, having a beam of 15 feet each, and drawing 4 feet 6 inches of water. One of these was lashed on each side, the other two being towed astern, and, though the weight of the whole must have been close upon 400 tons, and a considerable resistance was offered, also, by their form, the steamer towed them at the rate of 5½ miles an hour in slack water, or in 11 minutes between the two bridges, a distance of 1 mile.

These experiments having been considered in every way satisfactory, the Robert F. Stockton, of which the following is an illustration, left England for the United States in the beginning of April 1839, under the command of Captain Cram, of the American merchant service. Her crew consisted of four men and a boy, and, having accomplished the voyage under sail in forty days, Captain Cram was presented with the freedom of the city of New York for his daring in crossing the Atlantic in so small a craft, constructed only for river navigation.

In 1840, Captain Stockton sold this vessel to the Delaware and Raritan Canal Company, permission having been obtained (being British built) by a special Act of Congress, to run her in American waters, and her name was at the same time changed to that of the New Jersey. For many years she was in constant work as a steam-tug on the rivers Delaware and Schuylkill during the winter months, as she was capable of towing through the drift ice, where paddle-wheel steamers are of little use.

If we except the small vessel tested by J. Stevens[143] between Hoboken and New York in 1804, the New Jersey was the first screw-propelled vessel practically used in America, numerous experiments with the screw having been previously made without success, and she certainly was the first used for commercial purposes. The importance of the screw as a propeller having now been fully admitted in America, 150 vessels of a similar description were in less than ten years from that time employed in the United States; most of which continued to be in active operation in the carrying trade, returning large profits to their owners, particularly those employed on the great North American Lakes. Indeed, in 1848, thirteen screw-propelled vessels were employed on Lake Ontario, and only nine paddle-wheel steamers.

It is not my province to decide to whom the honour of the invention of the screw is due. It had engaged, as has been shown, the attention of various men in different countries for more than a century before it was applied to any useful purpose, and, like most other great inventions, has evidently been the production of many minds. I can, therefore, only deal with it as has been done in the case of the steam-engine itself, in its application to marine propulsion, by inquiring who it was that first, by practical tests, showed its superiority to the paddle-wheel, and that, for the purposes to which it has been applied, it could maintain such superiority over all other modes of propulsion. As this appears to me to be the only way in which this question can be fairly treated, I shall venture to state that, if Robert Fulton of America and Henry Bell of Glasgow are entitled, as I think they are, to be considered the first who put the paddle steamer into practical and continuous employment (I hold that James Watt and Robert Symington were its true inventors), it may, with equal justice, be said that to Captain Ericsson, Mr. Pettit Smith, and Mr. Woodcroft, the credit is chiefly due of having put the screw into working order so as to show how it could be profitably employed for the purposes of commerce or of the arts of war, though, at the time when Smith and Ericsson were practically illustrating the power of the screw, in their respective forms, that of Mr. Woodcroft, though well known, had not then been tried. In fact, his invention bears date antecedent to that of either of the others,[144] and proved equal, if not superior, when tested; indeed, it must have been considered so by the Admiralty, as it was fitted in the royal yacht Fairy, which, with the exception of the Rattler, and the Bee, of thirty tons, was the first screw-propeller in Her Majesty’s Navy: it was also about the same time applied to H.M.S. Dwarf. Mr. Woodcroft’s “varying-pitch screw-propeller,” patented by him in February 1844, of which the following is an illustration, was, certainly, in advance of any other at that time, and is, I believe, still considered the best and most useful type. In the account of it furnished by its able and ingenious inventor, it is said to be the “only propelling instrument of any description which has the peculiar and inherent property of acting with an increased impulse against the water from the leading part, first taking its action against the water to the end, however long or short such propeller may be upon its axis.”

However, be that as it may, when an impartial review is taken of all the facts, it may be said of Messrs. Woodcroft, Ericsson and Smith that, while each may be regarded as the individual author of their respective plans, conceiving as they did their designs apart from each other, we are indebted to them conjointly for this most valuable invention.

While the relative merits of the paddle-wheel and screw were being tested, the attention of scientific men was necessarily directed to the different forms of ships or lines best adapted to the various requirements of maritime commerce, which the introduction of steam had either created or materially developed. Vessels of every conceivable form, and of varied dimensions, have been in use from the earliest ages: we have had, of one sort or another, canoes, coracles, barges and yachts, coasters and Indiamen, with frigates and line-of-battle ships such as they were, almost from the dawn of history, and no doubt their owners and builders bestowed much thought and exercised considerable skill in their construction, so as to suit the varied purposes for which they were required; but it is only within our own time that a thorough scientific knowledge has been invited to aid in the construction of our merchant ships.

That knowledge has become much more necessary now than it ever was before. To construct an useful and first-class steam-vessel, we must first build a hull adapted to receive machinery, and then erect suitable engines and boilers with an appropriate propelling apparatus, combining the whole into a form such as will insure safety and speed, the requisite space for the crew, machinery, fuel, and stores, with accommodation for passengers and their numerous wants, and, also, sufficient space for a remunerative cargo.

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.