184-,>.] 



THK CIVIL EN(;lNEEll AND ARCHITECT'S JOURNAL. 



17 



gation, and to insure an average rate of ^'regress greater than that of 

 sailing vessels." 



This limit, be it observed, is one of expediency — not of abstract 

 practicability. To state the matter in other words — a certain deter- 

 minate proportion must be observed between the power and tonnage, 

 else the vessel will be incapable of carrying coals enough for the voy- 

 age, or her speed will be so defective as to give her no prominent ad- 

 vantage over sailing vessels. And the adherence to this proportion 

 involves the necessity of employing vessels of such magnitude as to 

 be of too expensive maintenance for the profits of an ordinary trade. 

 For as in a symmetrical vessel the resistance increases nearly as the 

 square of the increment of one dimension, and the capacity nearly as 

 the cube of the increment of the same dimension, so it is in a certain 

 point only in the divergence of those series where a result is obtain- 

 able, answerable to the conditions indispensable to .Atlantic steamers. 

 And that point is so high up in the series, the resistance and capacity 

 are both so great as to indicate the necessity of employing those levia- 

 than vessels, whose voracious appetite is unappeased by the expendi- 

 ture of all the proceeds of any merely commercial enterprise. 



"To arrive at a practical conclusion as to the major limit of a pro- 

 bable steam voyage under average circumstances of wind and water, 

 it will be obviously necessary that we should obtain some probable 

 approximative estimate of the impulsive virtue of a given quantity of 

 coals of average quality. The consumption of coals, other circum- 

 stances being the same, will be proportional to the power of the en- 

 gine, and it will therefore be sullicient to determine what is the average 

 rate of hourly consumption for each horse power in the machinery." 



A table of the performances of a number of ditlerent vessels between 

 1834 and the date of the Bristol meeting, but which we consider it 

 unnecessary to insert here, shows that the locomotive duty of the 

 Medea was greater than that of any of the rest ; the locomotive duty 

 as defined by Dr. Lardner being " the distance over which a ton of 

 coals per horse power is capable of propelling a vessel." 



Dr. Lardner proceeds — " To enable us to establish an analogy be- 

 tween 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 those 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 mo- 

 lion than that proper to the tropics, a relative atmospherical motion 

 is produced in a direction contrary to that of the earth's rotation. 

 Hence a nearly permanent wind is produced on each 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 Allantic between the shores 

 of Europe and (hose of North America. There arc 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 liikcs and primeval forests, supply a current of 

 cold air rushing into the warmer strata over the track of ocean between 



the Azores and the American coast. This current from the north-west 

 consequently modifies the re-action of the trades just explained ; the 

 result is wind blowing generally in the westerly direction, but varying 

 between north-west and south-west, and sweeping across the face of 

 the Atlantic throughout nearly the whole year. 



" Atmospheric didiculties 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 direc- 

 tion a little to the cast of north, and becoming more ami more westerly, 

 until it approaches within a short distance of the tail of the great 

 bank of Newfoundland, where it sets in due cast towards the Azores. 

 The width of this current at first one degree, gradually increases until 

 it exceeds two degrees. Independently of the difficulty presented by 

 the stream itself, the zone of the ocean marked out by it is character* 

 ised by weather so extremely unfavourable to navigation, that it is 

 cautiously avoided by all outward bound vessels. They invariably 

 either take a course so far north as to be clear of its influence until 

 they approach the western shores, where by taking a southerly direc- 

 tion they convert the westerly winds into favourable gales ; or on the 

 other hand proceed 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 New York packets, except they are reduced to a dis- 

 abled 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 land locked seas such as 

 the Mediterranean and the channels which intersect contiguous islands, 

 the effect of the wind in raising the waters is rapid and produces a 

 short and chopping sea highly unfavourable to steamers; but these 

 effects speedily subside, and in the Mediterranean especially they pro- 

 duce 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 eftects are incessantly, and considerably more disad- 

 vantage 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." 



It is right to observe that a " short chopping sea" is a rel.ative term, 

 having reference not merely to the nature of the waves, but the size 

 of the vessel. That which is a long swell to a row boat is a short 

 unfavourable sea to a small vessel, and that which is a long swell to a 

 small steamer, or even to a steamer of .')00 or 000 tons, may be a short 

 chopping sea to one of 2000 tons. The swell of tiie Atlantic therefore 

 may be of as prejudicial a quality to the large Atlantic steamers as 

 that of the Mediterranean, and of the channels is to the smaller vessels 

 navigating those waters. 



Another formidable objection to Atlantic steam voyaging arises 

 from the overwhelming force of the Atlantic storms. The shock of 

 masses of water roused into violent commotion by the accumulated 

 momentum of every wave in the whole three thousand miles of foam- 

 ing waters is nearly irresistible, and is productive of the most injurious 

 effects to vessels of large dimensions impelled by immense steam 

 power. We ourselves happened to see the Liverpool in dock after 

 an exposure to one of these Atlantic storms, and she was really little 

 better than a wreck. The straining she had undergone was incon- 

 ceivable : the seams of the deck had opened greatly, a great part of the 

 coppT had been detacheil from the bottom of the vessel in consequence 

 of the irregular movement of the planking to which it had been n.iiled, 

 and the oakum hung out of many of the seams in the exterior of the 

 vessel, even below the water line, from which the great straining had 

 displaced it. The " British Ijucen," it is well known has been simi- 

 larly injured upon more than one occasion, and the frames of the en- 

 gines of the Great Western have been all broken by the working of 

 the ship. The wear and tear arising from this source is infinitely 

 more to a long large steamer than to a compact well built ship; and 

 the danger resulting from the same cause is not inconsiderable. The 



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