48

HISTORY AND PROGRESS

does not in the same degree add to the strength; the uprightsection d i, being the only part in that position whichpresents the strongest form of section; this, however, aspreviously stated, being limited in height or downright pro-jection, has been cast upon the opposite side of the buoyingsection of the rail, shewn by a f, Fig. VIII. and a f a, Fig.VII., the form of this, as shewn in the latter figure, is suchas to secure equal strength in every part of the rail, beingdeeper in the middle, f, and tapering away in a parabolic orsemi-elliptic form, in both directions, to the ends of the rail.

This form of rail, with very trifling modifi-cations, constitutes the most modern plate rail;until very lately they were universally made ofCast-iron ; but, about a year ago, some wereformed of wrought-iron; the latter have as yet,however, been very partially used.

Soon after the introduction of cast-iron rails,a form of rail, called the Edge Rail,” wasbrought into use. Mr. W. Jessop, in 1789,formed the public Rail-road at Loughborough with this kind of rail ; the upper surface ofwhich was of an elliptical figure, with flangesupon the wheels to guide them upon the tractsof the road.

In the wooden Rail-ways, the upper railsw r ere convex on the surface, and upon one sideof the periphery of the wheels a flange project-ed downwards about an inch, which servedto keep the wheels upon the rail; when theplate-rail was introduced, the form ot the peri-