264 RAILWAY CONSTRUCTION. 



necessity, and those travellers who have had any experience of 

 railways under a tropical sun, will call to mind the celerity with 

 which the passengers seek such welcome shade. 



A very important item in the construction of a large terminal 

 station is the roof over the lines and platforma Wrought-iron 

 and steel can now be obtained in so many convenient sections, 

 and at such moderate prices, that timber-framed roofs, except 

 for very small spans, are now rarely used for railway work. 

 The metallic structure is much lighter in appearance and more 

 durable, besides being less exposed to destruction by fire. The 

 introduction of iron and steel has enabled roofs to be constructed 

 of very much larger spans than would have been prudent to 

 have attempted in timber ; at the same time it must be kept in 

 mind that, notwithstanding this increased facility of construc- 

 tion, the cost of a roof per relative area covered increases very 

 rapidly as the span increases. The extent of space to be roofed 

 over in some of our modern terminal stations is so large that the 

 question of roof-spans to be adopted has to be considered very 

 carefully. It has been argued by some that if the area be 

 divided out into small or moderate spans, the presence of the 

 rows of columns for supporting the roof might preclude the 

 possibility of any future re -location of the lines and platforms 

 except by an entire rearrangement of the roof- work. On the 

 other hand, it may also be stated that railway engineers have 

 now obtained such a thorough experience of the necessary relative 

 proportions of platforms and carriage-lines for large stations, as 

 to enable them to lay out these works without any risk of 

 requiring alterations for many years. 



There are so many descriptions of roof-principals used in 

 railway stations that it would be impossible here to introduce 

 more than a few examples. Figs. 387 to 405 illustrate by 

 diagram sketches a series of types taken from actual practice. 

 Fig. 406 gives more in detail the particulars of the roof-principal 

 of 60 feet span, Fig. 392. As will be noted from Fig. 406, the 

 width of 120 feet between the walls is divided into two spans 

 of 60 feet each, the ends of the principals in the centre of the 

 120 feet being carried on arched wrought-iron girders of 48 feet 

 span, supported on strong ornamental cast-iron columns placed 

 at 48-foot centres. The rain-water from the large centre gutter 

 is taken down inside the columns and conveyed away to drainage 

 pipes laid down for the purpose. The 60-foot principal above 



