224 Report on the Progress and State of Applied Mechanics. 



65. The Haeboxte Works of recent date ai'e remarkable rather for 

 magnitude than for novelty of principle. Some reference has already 

 been made to the methods employed for fomiding and building masonry 

 in deep water. With respect to those jetties, piers, and lighthouses, 

 which stand on posts or piles, allowing the waves to pass unresisted, 

 the most remarkable invention of recent date, is that of screw piles, by 

 Mr. Mitchell of Belfast. The knowledge of the true principles of 

 obtaining and preserving deep watee in tidal channels, has for 

 some time been gradually advancing ; and an excellent example of its 

 appHcation is afforded by the Clyde Navigation. Amongst recent har- 

 bour works of magnitude, may be mentioned those of Cherbourg, Ply- 

 mouth, Dover, Tynemouth, and Sunderland. 



66. Amongst Land Vehicles, Eailway Carriages may be specified. 

 The tendency of the present time is to increase their size, so as to 

 augment their accommodation for passengers, as compared with their 

 cost. On hnes with sharp curves, some advantages are possessed by 

 carriages constructed in the American style, of great length, sup- 

 ported at the ends by rollers and pivots, upon a pair of small four- 

 wheeled trucks. 



67. In Ship-building, the extension of the use of iron instead of 

 wood is well known ; but, on account of the difficulty of keeping the 

 bottoms of iron ships free from barnacles, there has been of late a cer- 

 tain disposition to return to the use of wood for sailing vessels. The 

 progress of improvement in iron ship-building is much retarded by the 

 manner in which the builders are restrained from exercising the skill 

 resulting from their experience and ingenuity, — being fettered in some 

 things by government regulations, and in others by conditions as to 

 tlae forms and proportions of ships, laid down by the purchasers of them 

 and by underwriters. Another cause which has for a time retarded 

 improvement in iron ship-building has been the practice of imitating the 

 structure of a wooden ship, with keel, ribs, and planking ; a construc- 

 tion which is the most suitable for timber, but quite unsuitable for 

 iron, as was well pointed out by Mr. Scott Russell at the meeting of 

 the British Association in Dublin. The Great Eastern is an admii-able 

 example of the use in ship-buUding of the true principles of construc- 

 tion in iron ; and it is to be hoped that other examples of the same 

 kind may be multiplied, and that all iron ships may be constructed so 

 as to give the greatest strength and capacity with the least weight, and 

 so to realize the great principle of economy. 



68. Besides strength and capacity, a ship requires stabiUty and speed. 

 The principles of the stabihty of ships were long ago investigated by 

 Bossut, and other French mathematicians, and successfully apphed to 



