218 Report on the Progress and State of Ajjplied Mechanics. 



by undermining it from within, whUe the building of the lining is con- 

 tinued at the top, until a firm stratum is reached, when the well is 

 filled with concrete, or arched over ; so that each well forms a piUar, resting 

 on solid gromid ; and on a sufficient number of such pillars, suitably 

 placed, the superstructure can be erected. This method has been fol- 

 lowed with success on the Indian railways. 



45. A method of making rousDATioNS in watee and mud, first 

 introduced at the new bridge over the Medway at Rochester, is now 

 coming into extensive use. A vertical cast iron pipe, extending from the 

 bottom to about nine feet above the surface of the water, and large enough 

 for men to work in, is bolted together in lengths, with internal flanges; 

 and on the top is bolted a cast iron bell, havmg within it a box with 

 double doors for entrance and exit, and a windlass and platform. A 

 steam engine forces au- into the bell until all the water is expelled from 

 the vertical pipe, and continues to force in a supply sufficient for the 

 workmen, who excavate the materials at the bottom, so as to imdermine 

 the pipe and allow it to sink, — passing themselves in and out, and 

 removing the materials, when required, through the box, which is so 

 contrived that only one box-full of compressed air escapes at each time 

 when the box and its doors are used. When the tube has sunk, so that 

 the lower edge of the bell is near the water, the compressed air is blown 

 off, the bell removed, a new length of pipe bolted on, the bell replaced, 

 and air again forced in ; and the operation proceeds as before, till a firm 

 stratum is reached, when the pipe is filled with concrete or with masonry, 

 so as to form a pillar to support the superstructure. This method has 

 recently been applied on a very great scale in Mr. Brunei's viaduct at 

 Saltash. 



46. The STEAM iiAMMEE has facilitated the making of foundations, 

 by its use in driving piles. 



47. For founding and building in deep water, improvements have 

 been made in Diting-Bells or Diting-Boats, by Dr. Payerne and by 

 Mr. Hallett, which enable those machines to rise, sink, move from 

 place to place, and otherwise manoeuvre under water, at the pleasure 

 of those within them. 



48. In Masonry and Brickwork, the gi-eatest works which have been 

 executed of late years, are remarkable rather in an architectural than in 

 a mechanical point of view, if we except some bridges, such as the two 

 principal bridges of Glasgow, — some large viaducts, such as that of 

 Ballochmyle, — some great towers, such as those ofWestminster Palace, — 

 some tall chimneys, such as that of St. Eollox and that of Mr. Towns- 

 end's works at Port-Dundas, — and the piers of some iron bridges, of 

 which the most remarkable for the maernitude of the undertaking are 



