60 Improvements bf the Port of London, 



ft ream, to the bold and ingenious labours of the Swifs car- 

 penter at Schaffhaufen. 



Bridges continued to be chiefly compofed of timber or of 

 flone, till of late years: on account of ceconomy, in fome 

 cafes, they have been built with bricks. 



Metals not being generally found in a pure ftate, require 

 much labour and expenfe to make them fubfervient to the 

 purpofes of man, and therefore, in the uncultivated periods 

 of lociety, were not applied to works of great magnitude; 

 but the important improvements in chemical and mechanical 

 knowledge, have, in a great degree, removed thofe difficulties, 

 and rendered them not only the mod powerful, but the moil 

 ufeful means of man. 



Iron being the mod abundant, cheap, and generally ufeful, 

 of all the metals, has of late years been applied in all works 

 where great ftrength was required in proportion to the weight 

 of the material : hence cylinders, beams and pumps for fteam- 

 engines, boats * and barges for canals and navigable rivers, 

 beams f and pillars for large buildings and_bridges, have been 

 conftructed of iron. 



The firft iron bridge we know of, is over the river Severn, 

 near Coalbrookdale, in Shropfhire ; it confifts of one arch ioo 

 feet and 6 inches in the fpan, and rifes 45 feet : there are five 

 ribs, each call in' two pieces, fecured where they join at the 

 crown of the arch by a call-iron key plate, and connected toge- 

 ther, horizontally and vertically, bv caft-iron braces, formed 

 with dovetails and forelocks; the ribs are covered with caft- 

 iron plates, and the railing to the fides is of iron : the total 

 weight of iron is 378^ tons. The project's being carried into 

 execution was chiefly owing to the genius and exertions of 

 Mr. John Wilkinfon and Mr. Abraham Darley, iron matters, 

 whofe fcientific knowledge and extend ve practice, in all that 

 regards the manufacture of iron, have long been known to 

 the public. The bridge was built by Mr. Abraham Darley, 

 and the iron work was caft at Coalbrookdale in the year 1779. 

 It was a bold effort; for, in the firft inftanceof adopting a new 

 material, they exceeded the fpan of the centre arch of Black- 

 'friars bridge, which had been considered as a great exertion 

 with ftone. 



• Mr. John Wilkinfon has conftrudted boats and barges of iron, fome 

 of which arc ufed on the river Severn, and the others upon the canals in 

 btaftbrdmire and Worcefterfhirc. 



f A large manufactory for i pinning; flax into thread, bv machinery 

 worked by a fteam-engine, has been eredted at Shrewsbury by Meffrs. Ben- 

 y.on, Marflvdl, and Bage, where there are four heights of floors, and a roof 

 compoiud of brick archts, which are fupported by caft-iron beams and pillars. 



The 



