(/HAP. xrr. 



THE MEXAI BRIDGE. 



and finished and proved at his works, under the inspec- 

 tion of a person appointed by the engineer. 1 



CUT SHOWING FIXING OF THE CHAINS IN THE KoCK. 



The mode by which the land ends of those enormous 

 suspension chains were rooted to the solid ground on 

 either side of the Strait, was remarkably ingenious 

 and effective. Three oblique tunnels were made by 

 blasting the rock on the Anglesea side ; they were 

 each about six feet in diameter, the excavations being- 

 carried down an inclined plane to the depth of about 

 twenty yards. A considerable width of rock lay be- 



1 The cross sections of the bars 

 forming the main chains were 3 \ inches 

 square ; they were proved to be 

 capable, according to Mr. Telford's 

 experiments, of bearing a strain of 

 not less than 87f tons before fracture; 

 but in order not to strain the iron un- 

 duly, the proof was limited to 35 

 tons, or about 11 tons to every square 

 inch of cross section. Every piece of 

 iron introduced in the work was sub- 

 mitted to this test by means of a very 

 accurate and powerful proving ma- 

 chine constructed for the purpose ; 

 while under the strain, it was fre- 

 quently struck with a hammer, and 

 after being proved, every separate 

 piece was well cleansed, put into a 

 stove, and when brought to a gentle 

 heat was immersed in a trough con- 



taining linseed oil. It was then taken 

 out after a short time, again put into 

 the stove, and, when dried, appeared 

 as if covered with varnish. A coat of 

 linseed oil paint was finally put over 

 all, and the iron bar was in this state 

 sent to the bridge for use. " No pre- 

 cautions were spared," writes Mr. 

 Telford, " to render every part per- 

 fectly true, and therefore secure; for 

 as any variation in the length of the 

 numerous bars would produce un- 

 equal bearings, each was subjected to 

 a fresh adjustment by means of a 

 steel model, upon which they were 

 bored when cold, so that a cross-bolt 

 passed through a certain number, in 

 most cases through eight bars, so as 

 to form four chains, thus accurately 

 attached to each other." 



