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seas not subject to any peculiar periodical difficulties. Of the nine thousand miles performed by the Medea, from which the average has been taken, about one-half was in the Mediterranean, and the other on the western coasts of Europe. The whole performance of the Dee was in the West Indies, making passages between the islands.
To enable us to establish an analogy between the performances of these vessels, and the circumstances under which a steamer would be placed in navigating the Atlantic, it will be necessary to explain some physical phenomena attending that ocean.
The general atmospheric currents which prevail in directions near and parallel to the equator, from east to west, called the trade-winds, would have a tendency to produce a derangement in the atmospheric equilibrium, if not redressed by a contrary effect elsewhere. It is known that these remarkable winds are produced by the influence of the solar heat upon the atmospheric belt included between the tropics, combined with the diurnal motion of the earth from west to east. The heated air, pressed upwards by its buoyancy, is replaced by currents from either hemisphere; which, carrying with them a less diurnal motion than that proper to the tropics, a relative atmospheric motion is produced in a direction contrary to that of the earth's motion. Hence a nearly permanent wind is produced on either side of the line, from east to west. As these currents approach the line, they gradually acquire the motion of the surface, which, combined with their mutually counteracting effect, produces those calms which prevail about the line, and which are only interrupted by the hurricanes, whirlwinds, and other violent atmospheric commotions, which are produced where the contrary tropical currents conflict, before their force is sufficiently moderated.
The stagnant atmosphere thus collected at the line, ascending by the effect of solar heat, returns from the upper regions towards the poles, and coming upon the surface in either hemisphere, brings with it the diurnal motion of the equator, which, being greater than that of the higher latitudes, prevailing winds are produced from the west. The agency of these causes is manifested in the westerly winds which prevail almost uniformly throughout the year in the Atlantic, between the shores of Europe and those of North America. There are other physical causes which mingle their effects with those to which we have just adverted. The extensive regions of North America, covered with immense fresh-water lakes and primeval forests, supply a current of cold air rushing into the warm strata over the tract of ocean between the Azores and the American coast. This current
from the north-west consequently modifies the reaction of the trades just explained; the result is-winds blowing generally in the westerly direction, but varying between north-west and southwest, and sweeping across the face of the Atlantic throughout nearly the whole year.
Atmospheric difficulties are not the only ones which the navigator has to encounter who crosses this extensive tract of water; the well-known Gulf Stream is a great ocean current issuing from the channel which separates Florida from the Bahama banks; taking first a direction little to the east of north, and becoming more and more easterly till it approaches within a short distance of the tail of the great bank of Newfoundland, where it sets in due east towards the Azores. The width of this current, at first one degree, gradually increases till it exceeds two degrees. Independently of the difficulty presented by the stream itself, the zone of the ocean, marked out by it, is characterised by weather so extremely unfavourable to navigation, that it is cautiously avoided by all outward bound vessels. They invariably take a course either so far north as to be clear of its influence until they approach the western shores; where, by taking a southerly direction, they convert the westerly winds into favourable gales; or, on the other hand, proceed, at first, southward, till they get beyond the lower limits of the Gulf Stream, and, taking advantage of the trades, make the western coast. This latter, however, is a route never adopted by the best class of the New York packets, except they are reduced to a disabled state.
The westerly winds, which we have described as prevalent across the Atlantic, are accompanied by a heavy sea, which is subject to scarcely any subsidence or intermission. In landlocked seas such as the Mediterranean, and the channels which intersect contiguous islands, the effect of wind in raising the waters is rapid, and produces a short and chopping sea, highly unfavourable to steamers; but these effects very speedily subside, , and in the Mediterranean especially, they produce but a slight influence upon the average rate of vessels when that average is computed from long-continued performances. On the other hand, the long swell of the Atlantic is not so unfavourable during its operation, but its effects are incessant; and considerably more disadvantage to a steamer will be produced by its continuance than any which the occasional roughness of the more contracted seas, to which we have referred, could give rise to.
To discover how far these various physical causes affect the navigation of the Atlantic, it will be necessary to enquire into the performance of vessels making passages between Great Britain and New York; and to obtain such extensive data as will obli
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terate from the computed average all accidental inequalities. It is well known that the outward voyage to the United States is considerably longer than the homeward; but we must determine the proportion between them with some degree of numerical precision.
Some of the finest and most efficient sailing vessels which have perhaps ever crossed the ocean, are the packet-ships called the Liners, which are the chief means by which the most respectable classes of passengers are transported between this country and New York. These vessels are built for the express accommodation of passengers who are able and willing to pay a high price for the most luxurious and expeditious means of transit between the Old and New World, Every thing is therefore sacrificed to their accommodation-all that art can effect to confer the quality of speed upon sailing vessels is brought to bear upon these ships. There are two lines of them; one between London and New York, the other between Liverpool and New York-the vessels departing weekly. We have obtained an account of the performance of the Liverpool liners for the last three years; and we find that the average time of the outward passage has been thirtyfive days and seventeen hours, and of the homeward passage nineteen days and seven hours,
If it be desired to obtain any approximate numerical estimate of the obstacles which steam power will have to overcome in a Transatlantic voyage, there are no grounds of reasoning except such analogies as we may be enabled to establish between the circumstances of wind and water upon the Atlantic, and those incidental to the seas already navigated by the most powerful and efficient steamers. We have shown that the steam-packets running between Falmouth and Malta, are inferior in their speed as well as in their locomotive duty to steamers of a larger class ; we shall therefore put aside those packets as giving a result unfavourable to the Atlantic enterprise. It has been stated that the Scottish steamers which run the longest class of passages, are among the finest and most efficient vessels yet constructed. They are unquestionably splendid vessels,* but still, none of them
*There are difficulties in obtaining exact information respecting all vessels belonging to private companies, and still greater difficulties in making public such information when obtained. These difficulties appear to be almost insurmountable, and inseparable from the very nature of private enterprise. Few of the proprietors of steamers know either the precise rate of their vessels or their consumption of fuel. If the passages be enquired after, the quickest are given instead of the average. If the conention of fuel be asked, the most favourable will be given.
are superior either in their powers of speed, or what is more important to the present question-their locomotive duty, to the Medea. Taking then this vessel as having the greatest locomotive duty of any respecting which we have yet been able to obtain information, we shall assume that a steamer constructed for navigating the Atlantic shall have, under like circumstances, equal efficiency: the question is, first, in what proportion should the difficulties of the outward passage to New York be estimated, as compared with the navigation in which the Medea had been worked? and, secondly, what tonnage and power could be given to a steamer to enable her to make that outward passage ?
The average or mean of the outward and homeward passages of the Liverpool liners would be twenty-seven days and a half. Now this mean is very nearly twenty-five per cent less than the average outward passage. It follows, therefore, that the average outward passage presents to a sailing vessel obstacles to expedition twenty-five per cent greater than the average of the two
The average of the outward and homeward Atlantic passages is evidently more unfavourable in a considerable proportion, than the average weather encountered by the Medea. This would be the case with respect to sailing vessels; but it must be still more so with reference to steamers. In assuming that the mean of the voyage between Liverpool and New York would fairly represent the circumstances of weather in the Mediterranean and on the coasts of Europe, we should be tacitly assuming, that the advantage gained by a steamer from the favourable winds in the homeward passage, would fully compensate for the disadvantage and delay produced by the adverse weather in the outward passage. This may be easily shown to be a fallacious assumption. In the first place, the heavy sea produced by these winds would be nearly the same impediment to the full efficiency of mechanical propulsion, whether in the outward or homeward passages; and would be so much greater if it were considered unadvisable to substitute the complicated feathering for the common paddle-wheels, The aid obtained by the engines, from the favourable winds, on the homeward passage, could not compensate for the obstruction which the same wind would offer on the outward passage; on any other supposition than that the velocity of the wheels might be almost un
registers are kept of these matters, they are so loosely and inaccurately managed, that nothing certain or satisfactory can be inferred from them.
limited-one which cannot for a moment be admitted. That the paddle-wheel should propel with the same energy when the wind is favourable as when it is adverse, it would be necessary to assume that the excess of the speed of rotation of the wheel above the progressive motion of the vessel through the water, should be the same in both cases-which it evidently cannot be. The absolute propelling effect, therefore, of the paddle-wheel, when the vessel goes before the wind, must be less than when she faces it. In a word, there is a certain speed of rotation, beyond which the engine cannot propel the wheel; and the nearer to this speed is the rate at which the vessel would be propelled by the wind alone, the less efficient will be the mechanical propelling power. The average or mean, therefore, of the outward and homeward passages of a sailing vessel must be more favourable than the mean of the like passages of a steamer. Without, then, admitting that the mean of these passages obtained from sailing vessels, will fairly represent the average which would result from the navigation of steamers, and rejecting still more strongly the conclusion that such an average, taken from the Atlantic weather, with sailing vessels or steamers, is of an equally favourable character with the average navigation of the Mediterranean, and on the coasts of Europe, let us assume for a moment such to be the case; because, as the conclusion at which we shall arrive will be the one to which this supposition is most unfavourable, it will give us an argument a fortiori in support of it.
Taking, then, the ground of argument used at the Bristol meeting, let us suppose that the outward passage to New York is twenty-five per cent worse than the average weather to which the Medea was exposed. The locomotive duty of a ton of coals in that vessel being about two thousand miles, it would be fifteen hundred miles for the outward passage. The distance between Liverpool and New York being about 3200 miles, the quantity of coals necessary for the whole passage, exclusive of spare fuel, would be therefore two tons and one-tenth per horse power. If we allow twelve per cent of this quantity of coals for spare fuel for emergencies, we shall have, for the total charge of fuel necessary to be supplied to the vessel, two tons and four-tenths per horse power.
The Medea is a vessel of 800 tons measured capacity, and two hundred and twenty horse power. Her machinery, including the boilers, occupy 220 tons of her capacity. Two tons and four-tenths of coals per horse power would occupy about 539 tons. Thus, of her entire capacity 750 tons would be occupied by the machinery and fuel, exclusive of passengers or cargo; and