1855.] 



BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



145 



,tiou imposed on skips tliat were not built of certain sliapes, possessed 

 neither the requisite properties of stability nor winwardness, and Trere 

 very slow ; they were built solely with a view to liold the greatest 

 amount of cargo within a given superficies, without regard to the other 

 qualities of a ship. In smuggling and piratical vessels the true prin- 

 ciple of ship building, for acquiring speed, had however been long 

 introduced before the subject was taken up by the British Association, 

 and the wave principle of construction had thus been established by 

 extended experiments on a large scale. A fine concave entrance, 

 instead of a bluff round bow, is now generally admitted to be the best^ 

 and, in addition to the shape of the water line, it had been found that 

 length of the body of a ship facilitates its passage through the wa- 

 ter, by allowing a longer time for the particles of the fluid to separate. 

 A ship with a tine concave bow, a long body, and a comparatively 

 round stern, Jlr. Russell said, cleaves its passage through the water 

 without raising a wave in front to obstruct its course. No steam ship 

 that is not 180 feet long can be propelled at a speed of sixteen miles 

 an hour without a great expenditure of power ; and 400 feet is the 

 shortest length f jr a ship that is intended to be propelled at so high a 

 speed at twenty-four miles .an hour. As an illustration of this rule, it 

 was mentioned that the Himalaya, which is 365 feet long, attains the 

 greatest speed for the power employed of any merchant ship. In the 

 construction of large ships, however, the builders were met •with the 

 difficulty of not being able to find wood of sufficient size for the re- 

 quisite strength, since no means have y-X been invented of joining 

 pieces of wood together so as to give them the same strength as the 

 whole timber This want of material of sufficient size was supplied 

 by using iron, for the joints can be made as strongly as the whole 

 plate, or plates of metal of any required size can be rolled for the pur- 

 pose. This facility of increasing the size of the material is the prin- 

 ciple advantage derived from the use of iron, which affords facilities 

 for constructing ships of any size ; and it is of that material that the 

 great ship, now building in London for the Eastern Steam Navigation 

 Company, is to be constructed. Mr. Russell complimented Mr. Bru- 

 nei for the engineering skill and ingenuitj' he had displayed in leading 

 the way in the construction of large iron ships ; and he alluded to the 

 forebodings of disaster on former occasions, when the Great Western 

 and the Great Britain were built, which forebodings events had shown 

 to be groundless ; and he felt confident that the similar forebodings 

 which some people had expressed of the still larger ship now being 

 built would be equally fallacious. Mr. Russell said he wished it, 

 however, to be understood that he did not recommend the general 

 adoption of such large ships. The size of the ships ought to be suited 

 to the trafiic and the distance ; but the point he contended for was, 

 that it is only by employing very large ships that steam navigation to 

 distant parts of the globe can be profitably carried on. A steam-ship 

 to Australia, if it were not large enoilgh to carry sufficient coal for the 

 voyage, had to take' in a supply over and over again, and at each sta- 

 tion the cost of the coal was increased by conveying it to the different 

 stations. Under such disadvantages no freight could pay the cost of 

 conveyance ; and in order to remove them, it was necessary to build a 

 ship of sufficient size to carry a supply of fuel for the voyage out and 

 back again, or equal to circumnavigating the globe. An extremely 

 fine entrance was another of the characters which the large ship now 

 building would possess, so as to enable it to move through the water 

 with the greatest attainable velocity with a moderate amount of steam 

 power. With these advantages it was expected that the ship would 

 accomplish the voyage to Australia in thirty or thirty-three daj-s. It 

 would easily carry six thousand tons, besides its requsite quantity of 

 coal ; and would have excellent accommodation for 500 first-class pas- 

 sengers, 000 second-class, and 1.000 third-class passengers. It would 

 be 675 feet long, 83 feet in breadth of beam, and 60 feet deep ; and 

 though so large that St. Geoi'ge's Hall is small in comparison, it is the 

 smallest size that could do the work required with speed and economy. 



Mr. Fairbairn said Mr. Brunei had shown him the plans ; and 

 though he had at one time thought a ship of that size would be too 

 large for strength, he had, after examination of the plans, arrived at 

 the opposite opinion. He had now no doubt that the ship would be 

 perfectly strong, and be able to bear a gale of wind without bending. 

 It was built on the same principle as the Britannia Tubular Bridge ; 

 and when it was perceived that that mode of structure is able to sus- 

 tain a bridge without any support in the middle, there cimld be no 

 doubt that supported as the ship would be by the water, it would un- 

 der all circumstances bo able to bear the strains to which it might bo 

 subjected. 



Mr. Nasmyth explained a plan for destroying ships bv means of a 

 4 



marine mortar fixed at the bow of a strongly built vessel to be propell- 

 ed by steam power; He proposed to place in the bow of the vessel, 

 ana projecting about two feet beyond it, a case large enough to con- 

 tain about six hundred weight of gunpowder. A percussion ball was 

 to be inserted at the back of the reservior of gunpowder to explode at 

 the instant that it struck against the ship to be destroyed. The mor- 

 tar vessel was to be built of blocks of timber, so strongly as to be able 

 itself to resists the effects of the explosion, which would completely 

 destroy the enem3''s ship. Such a marine mort.ar, it was stated, could 

 be amply manned by " three brave fellows," who would be secured 

 from danger by the strength of the ship and its recoil, and by them 

 occupj'ing a position least exposed to injury, even should the explosion 

 do damage to the parts nearest to it. 



Mr. Nasmyth described a Lightning Conductor for Chimneys, which 

 he conceived affords more perfect insulation, and is therefore safer 

 then those in common use. The present practice is to fix the conduc- 

 ter outside the chimney by metal holdfasts, by which means during 

 severe thunder-storms chimneys are often damaged by the lightning 

 entering at the points of attachment and displacing the bricks. In the 

 method of fixing the conductor recommended by Mr. Nasmyth the metal 

 rod is suspended in the middle of the chimney by branching supports 

 fixed on the top. A conductor of this kind had proved efficient in 

 storms which had severdy injured other chimneys in the neighbour- 

 hood that were protected in the usual manner. An experience of 

 eighteen years had tested the superiority of the plan. 



Prof. Faraday, on being called on for his opinion, said that he re- 

 commended that lightning conductei-s should be placed inside instead 

 of outside of all buildings. He had been consulted on that point when 

 the lightning conducter was fixed to the Duke of York's Pillar, and he 

 advised the placing it inside, but his advice was not taken, and the 

 rod was fixed outside, to the great disfigurement of the column. All 

 attachments of metal to or near the conducter are fead, unless there be 

 a continuous line of conduction to the ground. He mentioned the in- 

 stance of damage done to a lighthouse in consequence of part of the 

 discharge lightning having passed from the conductor to the lead fas- 

 tening of the stones. The practical question for consideration by the 

 Mechanical Section was, how far they could safely run lead between 

 the stone of such a structure, for if it were done partially, leaving a 

 discontinuous series of such metallic fastenings, there would be great 

 d.anger of the stones being displaced by the electric discharge. When- 

 such fastenings are used, care should be taken that they are connected 

 together and with the earth bj' a continuous metallic conducter. Some 

 persons conceived that it is desirable to insulate the conducter from 

 the wall of a building by glass, but all such contrivances are absurd, 

 since the distance to which the metal could be removed from the wall 

 by the interposed insulator was altogether insignificant compared with 

 the distance through which the lightning must pass in a discharge 

 from the clouds to the earth. On being asked whether a flat strip of 

 copper was not better than a copper rod. Prof. Faraday said the shape 

 of the conducter is immaterial, prorided the substance and quality of 

 the metal are the same. 



A communication from Mb. Sewell, on Boiler Explosions, gave 

 rise to a discussion on the causes of such explosions, and on the 

 effect of percussion in weakening the strength of iron, in which 

 Mr. Fairbairn, Jlr, Roberts, Mr. Hopkinson, Mr. Oldham, and 

 other members took part. Mr. Fairbairn said, that, so far as 

 his experience went, the explosions of boilers generally occur 

 at the moment the engines start ; in consequence of the sudden 

 rcneration of steam by the increased motion given to the water. 

 With respect to the weakening of railway axles by use, he con- 

 ceived that effect to be produced rather by the continuous bindings 

 of the metal, however small thcj- may be, which give a set to the 

 fibres and increase the liability to break. Boiler-plates are also 

 frequently injured by the operation of punching for melting. Mr. 

 Roberts attributed boiler explosions in most instances to the defective 

 construction. He was of opinion that in rivctting boiler plates tho 

 rivets are seldom made large enough, large rivets being much stronger 

 than small ones. — Mr. Clay said the crystalline structure of 

 wrought iron acquired by long continued percussion might be restored 

 to the fibrous state by reheating. Mr. Oldham considered it would be 

 of advantage to reheat the axeltrecs of locomotive engines after they 

 had run for some time, so that the fibrous structure, from whatever 

 cause it was rendered cr^'st-allinc, might be restored. — Mr. Roberts 

 was not disposed to admit that any change is produced in the quality 

 of iron by wear. If tho iron were of good quality and perfect at 

 first it would remain so till it was worn out. Ho observed that bars 



