218 CORNISH VIADUCTS. 



There were originally forty-two viaducts in the 66 miles 

 on the Cornwall Railway between Plymouth and Fal- 

 mouth, exclusive of Saltash Bridge ; and their total length 

 amounted to about 4| miles. On the West Cornwall Rail- 

 way, between Truro and Penzance, the viaducts are ten in 

 number. 



All the old viaducts were constructed for a line of single 

 broad, and measured, as a rule, 14 feet between the parapets, 

 a width that would never be tolerated by the Board of Trade 

 now-a-days. Some of these were constructed entirely of 

 timber ; but the greater number consist of masonry piers, 

 from the tops of which timber struts radiate and support the 

 beams which carry the decking. They were designed by 

 the great Brunei, and although they are unfortunately built 

 of such a perishable material as wood, they are beautifully 

 proportioned to the work they have to do. Doubtless the im- 

 mense cost of the railway, amounting to £30,000 per mile, — 

 a very large sum for a single line in those days — precluded 

 him from using anything more durable. The wooden viaducts 

 of course require continual watching and constant renewals, 

 which become proportionately greater and greater the older 

 that they grow. The timber used in their construction and 

 subsequent renewal is Quebec yellow pine, treated with Kyan's 

 process, i.e. soaked in a solution of corrosive sublimate. This 

 process will preserve the wood very fairly, provided it be in 

 a dry situation, although it fails under water, and the corro- 

 sive sublimate is apt to volatilise. Kyanising was preferred 

 to creosoting on account of the liability of creosoted timbers to 

 catch fire from the sparks of a passing engine. As it is, a large 

 tub of water is placed at each end of the viaduct, in which 

 a swab is kept ready for any emergency. The platelayers 

 keep a good look out on the viaducts ; and if, after the 

 passage of a train, they observe smoke rising from the 



