MEANS OF COMMUNICATION. 19 
entirely abandoned since the advantages of wrought-iron rails have been 
fully recognised. 
The requisites of a good rolled rail are the following: 1. It must be rolled 
at an equal temperature throughout, and be entirely free from flaws. 2. 
The profile must be precisely the same at both ends, in order to allow per- 
fect fittings to be made. 3. The rail must be perfectly straight, and must 
have a suitable form. 4. It must offer sufficient surface to the driving 
wheels without at the same time producing too much friction; the surface 
is therefore generally slightly convex, in order to fit the conical tire in some 
measure. 5. That cheek of the rail which is exposed to the greatest pressure 
must be sufficiently strong not to break, and somewhat rounded, in order to 
correspond to the flange of the wheel. 
For the system of interrupted supports (pl. 2, jig. 32), the form and weight 
of the rails depend on the weight of the locomotives to be employed, their 
required speed, and the distance between the supports, as no flexure should 
take place. Various forms of rails have been used; those most generally 
employed now have a broad base, an oval top, and are from 3 to 5 inches 
high. A weight of 16 or 17 pounds per foot is generally deemed sufficient ; 
rails of much less weight have been employed on roads over which no very 
heavy trains are transported. The usual length of rails is 15 or 18 feet, and 
the ends meet at right angles, although an angle of 45° would be preferable, 
as diminishing the shock in passing from one rail to the next. 
The fastening of the rail and chair has been effected in many different 
ways; at present it is simply done by fastening the rails to the sills by 
means of spikes, the heads of which lap over the base of the rail, and at 
the ends only iron plates with projections that hold down the rail are used. 
Some of the more complicated chairs are shown in pl. 2; fig. 33 is a cast- 
iron chair of the London and Birmingham road, the manner of fastening 
which has been referred to above; jig. 34 shows Hartley’s chair for the 
Manchester and Bolton Road, which is fastened with spikes, ¢, the dotted lines 
showing the fastening between the chairs; the rails here weigh 20 pounds 
per linear foot. /%g. 36 represents the chair and rail on the Northern road 
in Austria, where the rail @ is held in the chair } by the heads of screw- 
bolts ec. ig. 37 is a cast-iron bridge-rail and chair of the Providence (R. 1.) 
road. The shape of the spikes is shown in jig. 35. F%g. 42 shows Steven- 
son’s attachment of chair and rail by which he intended to obviate the 
existing imperfections, but which was found too complicated and requiring 
too much accuracy in the execution for practical use, although well calculated 
to answer its purpose ; @ is the rail, bthe chair, ¢ the wedges, d the spikes, &e. 
The method of fastening the rails in the chairs by means of wedges of 
wrought-iron has proved to be imperfect, the wedges being loosened by the 
vibration of the track caused by the passage of the trains. The wedges in 
jig. 33 are of oak-wood prepared with a solution of corrosive sublimate (kyan- 
ized ) and compressed by hydraulic pressure ; these also are found to become 
loosened, and require constant driving, besides having other disadvantages. 
Wedges of tempered cast-iron have been employed with the best success. 
The foundation for a superstructure on the plan of continuous support for 
599 
