104 Rev. Mr Adamson on the extent of our 
7 tons in weight, in constant employment upon them for above 
two years. 
The duration of the rail ought to be determined by the pe- 
riod during which the upper part retains sufficient thickness to 
support the pressure of the wheel, without being broken or fold- 
ed down ; and if it be found, that, in the malleable rails, the un- 
der part decays too rapidly, then, as much iron must be added, 
beyond what is necessary for the due strength of the rail at first, 
as will enable the keel to retain its requisite strength and stiff- 
ness, until the upper part be worn away. Though somewhat of 
the strength and stiffness be lost, in a form of uniform depth, 
compared with that which is deepest in the middle between the 
points of support, when the quantity of iron is the same, it may’ 
perhaps be found advisable to relinquish the vertical undulations 
in the keel ; in order that less surface and fewer angles may be 
exposed to the influence of moisture. This would be most ad- 
vantageously effected, by having a keel of uniform depth, ex- 
panded into a cylindrical form at its under surface. We should 
also, then, have a neat and convenient method of attaching the 
rails to the blocks on which they rest : for a cast-iron chair or 
pedestal, formed so as to embrace this cylindrical part, might be 
slid on at the end of the rail, and pushed along to its proper 
place, where it would keep hold of the rail without pins or 
wedges. This sort of chair could be so formed, as to obviate, 
to a great degree, the consequences of the partial displacement of 
the blocks. The rail would have also the power of expanding 
longitudinally, without producing any derangement, and thus, 
on straight lines, very considerable lengths of the rail might be 
welded together, without inconvenience. 
The breadth of the tram of the edge-rail is never, as far as I 
have seen, above inches ; and no such rule is observed, as 
that which Mr Tredgold mentions, viz. 46 That the breadth in 
inches should be twice the weight upon one wheel in tons.” 
The rule is founded on the circumstance, that the loaded coal- 
waggons, in the neighbourhood of Newcastle-upon-Tyne, gene- 
rally weigh four tons, and the rails are almost always about & 
inches broad, — but along the same rails roll the engines also, 
carrying about twice the weight of a waggon. In fact, the rails 
have been gradually increased to their present breadth, with the 
