RAILWAY CONSTRUCTION. 289 



Opinions as to the most convenient position and use of turn- 

 tables have undergone a considerable modification during the past 

 twenty or twenty-five years. Circular and semi-circular running- 

 sheds for engines, as in Figs. 436 and 437, are not so often 

 adopted now as formerly. Although compact and accessible in 

 theory, they possess the one great drawback that when the turn- 

 table in the centre becomes deranged by wear or accident, none 

 of the engines on the standing-lines inside the building can be 

 taken out until the turn-table is again put into working order. 

 A stock of from twenty to thirty engines might thus be put en- 

 tirely out of the service for a day or more. This objection is 

 considered to be of so serious a nature that running-sheds are 

 now almost always constructed of rectangular form, of which 

 Fig. 438 is a type. 



With this description of shed, the lines of rails are laid down 

 parallel to one another, and the engine turn-table is placed on a 

 line separate and distinct from those lines forming connections 

 with the shed. 



Where there is a large goods traffic, an endeavour is generally 

 made to so lay -down the goods-sheds and approach lines and 

 sidings, that the full complement of waggons may be shunted in 

 or out of the shed at one operation. This arrangement, which 

 dispenses with turn-tables altogether, admits of the ready 

 removal of a central or far-end waggon, without the necessity of 

 taking out so many others in front one by one over the turn- 

 table. At the same time, there are large numbers of these 

 waggon turn-tables in use, and there are many cases where access 

 to side sheds or detached stores can only be obtained by turn- 

 tables. 



A goods-shed and lines laid down with turn-tables, as in Fig. 

 439, will always be more tedious and costly to work than one 

 laid down with direct through lines, as in Fig. 440. Should 

 either of the turn-tables shown on Fig. 439 get out of order and 

 become incapable of turning, then the entire side of the shed 

 controlled by that table will be rendered useless until the defect 

 be remedied. 



Engine turn-tables are rarely made with more than one road 

 on the top. The most modern types generally consist of two 

 strong wrought-iron or steel-plate girders well braced together 

 and securely attached to a middle framework which rests on 

 and revolves round a centre-piece fixed on a solid foundation 



