156 ON THE ENGINEERING MANUFACTURES 



sources, to the working of machines upon the system introduced by Sir 

 William G. Armstrong, no better reference can be made than to the com- 

 plete and extensive works erected upon the lead mines at Allenheads. 

 The hydraulic machinery is therein employed in rising materials from 

 mines ; in giving motion to machines for washing, separating, and 

 crushing ore ; in pumping water, and driving saw mills and the 

 machinery of a workshop. 



The most recent application of water power at these mines deserves 

 especial notice from its novelty. The district upon which the 

 several new works are placed, is void of falls of sufficient altitude 

 for working the engines and machines directly, but a river runs 

 through the district which is suitable for overshot wheels, and 

 through such mediums the stream is made to force water into 

 accumulators, thus generating an intensified power, which is utilised by 

 compact machines distributed in situations most convenient for their 

 several duties. The principal objects "sought in thus intensifying the 

 pressure is to lessen the size of the pipes, cylinders, and valves of the 

 machines, and to gain more rapid action, and also by so reducing 

 the size of parts, to effect a saving in outlay upon the work generally. 



Iron Bridges, Viaducts, Lighthouses, &c. — The art and manu- 

 facture of iron bridge building, and of other similar iron structures, 

 which form such an important feature in railway construction and 

 harbour improvements, are followed to a considerable extent by several 

 engineering firms in this district. 



The following brief notice of some of the most important of these 

 works can only be taken as an index of the resources of the district in 

 this direction. 



That noble structure which spans the river Tyne, and forms a com- 

 munication of road and rail at a high level between the towns of New- 

 castle and Gateshead, emanated, as is well-known, from the same 

 practical mind and genius that, with dauntless courage and rare skill, 

 threw railway bridges across the Menai Straits and the St. Lawrence 

 River. 



The superstructure of the High Level Bridge was executed by Messrs. 

 Hawks, Crawshay, and Sons, of Gateshead. This firm has recently 

 erected the cast-iron bridge at York, from the designs of Mr. Page ; it 

 spans the river Ouse in one arch of 172 feet in width. Also the new 

 bridge at Sunderland, which consists of a single arch of about 237 feet 

 span, at a level of about 90 feet above high water mark. A melan- 

 choly interest is attached to this bridge, it being one of the very last 

 works designed and undertaken by the late Robert Stephenson. 



Messrs. Hawks, Crawshay and Co. likewise ^constructed the wrought 

 iron gates for the Northumberland Docks, and the iron lighthouses at 

 Gunfieet, Calais, and Harwich ; and supplied the iron pier at Madras, a 

 work of considerable magnitude. 



Messrs. Robert Stephenson and Co., have been engaged upon the 



