34 ANNUAL OF SCIENTIFIC DISCOVERY. 



engineer below, helmsman at the wheel, and look-out man at the bows. In 

 iron vessels great precautions being necessary to prevent the compass from 

 being influenced by the mass of metal in such attractive proximity, various 

 experiments have been made with the view of discovering the best mode of 

 overcoming this. It was originally intended to locate the compass upon n, 

 stage, forty feet high, but this plan has been abandoned, and a standard 

 compass will be affixed to the mizzen-mast, at an elevation beyond the mag- 

 netic influence of the ship. 



The preparations made for launching the "Leviathan" are of a novel 

 character, and have been described as follows : 



Two strong and powerfully-built tramways have been constructed, running 

 from under the fore and aft portions of the vessel down to spring tide low- 

 water mark. Each of these ways is 300 feet long by 120 wide, and the dis- 

 tance between them is also about 120 feet. To guard against the shifting 

 nature of the river mud, the ways are constructed with unusual solidity and 

 strength. The foundation of each is formed upon seven rows of piles, the 

 four outside rows being driven in at three feet intervals, and the inner rows 

 at six feet. These piles are all forced home to the gravel of the river's bed, 

 so that they graduate from thirty-two feet long under the ship's bottom to 

 ten feet at low-water mark. To both sides of the pile-heads strong timbers 

 are securely bolted, and the whole area covered with concrete to a thickness 

 of two feet. Above the concrete longitudinal timbers of great strength are 

 secured at intervals of three and a half feet, and run the entire length. Over 

 these again are transverse timbers, three feet apart, bolted down, to keep 

 them fixed under the pressure they will have to bear, and to prevent them 

 floating at high tide. On these, but running straight to the water, railway 

 metals are screwed at intervals of eighteen inches. The rails complete the 

 launching ways, which thus form a massive road, stretching from under the 

 ship to low-water mark, at an incline of one in twelve. Down these ways the 

 vessel will be slowly lowered into the water on the cradles under her, which 

 are constructed of large hulks of timber, wedged with a ponderous machine 

 like a battering-ram, so as to perfectly fit the ship's bottom. The timbers 

 are laid principally athwartships, with longitudinal beams fastened to the 

 outer sides, and all are bolted together, and loaded with iron to prevent their 

 floating with the vessel. The bottom of the cradle consists of iron bars, 

 placed at intervals of a foot, and with their edges carefully ground off, so as 

 to offer no resistance to the metals over which they will have to pass. Both 

 launching ways rise slightly in the centre, in order to allow for the depres- 

 sion which is certain to be produced by the passage of such an enormous 

 weight over their surface. Before the launch the metals will be thickly 

 coated with a composition of tallow and black lead, so as to offer no ob- 

 struction. 



The chief points upon which the energies of Mr. Brunei have been concen- 

 trated were, first, to overcome the momentum of such a mass down an in- 

 cline of one in twelve, and prevent her, when once in motion, from dashing 

 entirely away ; secondly, if stopped from any cause upon the wa} r s, to pro- 

 vide sufficient purchase from the water to slowly pull her into motion again. 



