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On the Effects of the Curmture of Baihvays. By Edward Sang, 

 Esq., Civil Engineer, Edinburgh, M. S. A. Communicated 

 by the Society of Arts.* 



The prodigious velocity which is now attained on railways, 

 brings out prominently all the defects of their construction, 

 and renders it necessary to attend to every minute circum- 

 stance. It is well known that when a railway train is moving 

 upon a curve, there is a tendency to go off the rail, and to con- 

 tinue the rectilineal motion. To prevent the bad effects of 

 this, the outer rail is raised to such a degree as that the line 

 laid across the rails may be perpendicular to the resultant of 

 gravity, and the centrifugal force. This precaution completely 

 removes all tendencyof the waggons to move off the rail, and 

 all pressure against the ends of the axes. The point to which 

 I wish to draw the attention of the Society is the transition 

 from a straight line to a curve, or from one curve to another. 



It is considered by some to be sufficient that the straight 

 part of the rail be tangent to the circle which forms the curve ; 

 or that the circular parts of the rail have a common tangent 

 at their junction. By this means any sudden angle is avoided ; 

 but this is far from sufficient for the exigencies of railway 

 travelling. 



To see the nature of the defects of this plan, let us follow 

 a waggon in its course from one direction to another. The 

 instant that it leaves the straight line and comes upon the 

 circle, there is the centrifugal tendency ; and there must be 

 a rise in the outer, or a depression in the inner rail. Suddenly 

 the passengers, endeavouring (without being aware of it) to 

 continue moving in a straight line, feel themselves pressed to 

 the one side of the carriage — slightly it may be — 'but still sud- 

 denly. The rise in the rail cannot be instantaneous ; and 

 thus, either before or after the change of curvature, there is a 

 want of proper adaptation. Such must necessarily be the re- 

 sult wherever the transition from one degree of curvature to 

 another is sudden. 



This inquiry therefore offers itself ; What ought to be the 

 nature of the curvature of railways ? 



* Kead before tUe Society of Arts for Scotltmd, 27tU May 1840. 



