RAILWAY CONSTRUCTION. 309 



a fairly long wheel-base, retaining their united weight for 

 adhesion. The four-wheel bogie truck in front forms a valuable 

 path-finder to the engine, both for passing round curves or on 

 straight line. This class of engine is very serviceable for various 

 kinds of traffic, and is particularly suitable for lines where the 

 rails and fastenings are comparatively light. In the example 

 shown, the flanges are turned off the centre pair of coupled 

 wheels ; but for lines where the curves are of small radius, the 

 flanges may be turned off the leading pair of coupled wheels, 

 instead of the centre pair, to reduce the length of rigid wheel- 

 base. This type of engine has latterly been introduced on 

 various European and foreign railways, and recently on the High- 

 land Railway of Scotland, as shown in Fig. 470. The writer has 

 had engines of this class under his charge abroad, and found 

 them to be most useful for heavy passenger and goods-train 

 service. They run very steadily, are easy on the permanent 

 way, and light in repairs. As they become better known they 

 will be more appreciated, and will doubtless before long super- 

 sede in many cases the rigid six-wheel-coupled goods engine. 

 The principal objection of any importance that can be raised 

 against them is that on many lines the present engine turn-tables 

 are too small for such long engines ; but it would be far more 

 economical in the long run to enlarge a few turn-tables than to 

 continue the adoption of rigid engines which from their form 

 and arrangement tend to unnecessary wear to themselves and 

 the permanent way. 



Fig. 476 shows an average sample of the ordinary six- wheel- 

 coupled goods engine in use on [so many of our home railways. 

 Where the curves are easy and the permanent way strong, the 

 drawback of the long rigid wheel-base may not be so apparent ; 

 but for a line abounding in sharp curves, perhaps no more 

 destructive machine could possibly be devised than the ordinary 

 six- wheel- coupled goods engine. Without any flexibility, forced 

 along with great power, and too often driven at unnecessary 

 high speeds, engines of this type have too small a margin of 

 safety when traversing the curved portions of the road. A 

 slight unevenness in the rails, or a sharp flange on the wheel 

 may supply all that is wanting to cause the engine to leave the 

 track, and the probability that such risks are more common than 

 is supposed, is far from satisfactory. The great weight of the 

 engine doubtless tends to keep it on the track, but the rapid 



