CURVES-MANUFACTURE OF RAILS-FISH-PLATES-FASTENINGS-
KEYS-SUPER-ELEVATION-CURVE OF ADJUSTMENT.

IN my last lecture I brought down my description of the railway to the completion of the ballast.

The weights which rest on the small upper surface of the rails have to be distributed over a much larger surface of the ballast, which will be sufficient to bear the weight, just as we make large footings or foundations to distribute the weight of any structure over a large area. This distribution of weight is effected in rare cases by making the lower part of a specially designed rail so broad as to afford sufficient bearing area on the ballast, but ordinarily by introducing between the rail and the ballast intermediate appliances, of which sleepers and chairs are the most important.

An example of a rail made with a sufficiently broad base is the saddle-back,' or 'Barlow rail' (Fig. 27), which was designed to dispense with sleepers and chairs altogether. The rail is laid di

FIG. 27. Barlow rail.

rectly on the ballast, and the ballast is intended to completely

fill the inside of the saddle-back. The bearing area on the

PERMANENT WAY-RAILS.

75

ballast can no doubt in this way be made large enough to support the loads coming on the line, but the Barlow rail, unless its two sides be held fast, is vertically weak; while unless the ballast be kept absolutely tightly packed into the rail the wings of the rail spread elastically, and, working in and out, gradually displace the ballast beneath them. The Barlow rail has been largely used at home and abroad, and was thought at one time likely to form a very desirable and efficient description of road, composed of lasting materials with a minimum number of parts and fastenings; but experience has shown that so far at least as it has up to this time been used it leaves much to be desired, and that it is not well fitted for high speed or for heavy traffic.

Of other rails I need only mention three kinds, all of which require the addition of some kind of sleeper to distribute the weight upon the ballast. These are

(a) The double-headed rail (Fig. 28), which has to

I I

FIG. 28. Double-headed rail. FIG. 29. Flat-bottomed rail. FIG. 30. Bridge rail.

have chairs, as they are called, to keep it upright in place on the sleeper; (b) the flat-bottomed or Vignoles rail (Fig. 29), which requires no chair, but rests directly on the sleeper; and (c) the bridge rail (Fig. 30), introduced by the late Mr. Brunel for use with longitudinal sleepers. I will describe the special characteristics of each of the above well-known sections of rails further on, and after I have referred to some of the other parts of permanent way.

Sleepers in the present day are of wood or of

iron, and there are in general use but three kinds : 1. The wooden longitudinal sleepers (Fig. 31), which,

FIG. 31. Longitudinal sleeper road.

parallel to the line, extend under the whole length of each rail, thus giving continuous support to the rail throughout its length. 2. The wooden cross sleepers (Figs. 22 and 23, page 58), which, transverse to the line, support the

rails at intervals, each sleeper supporting one point of each of the two rails forming one line of way. 3. The iron-pot sleepers (Fig. 32), which are placed at intervals under each rail, each pot supporting one rail at one point.

Chairs, Fig. 36 (page 84), which, as I have said, are employed almost exclusively in connection with double-headed rails, are usually made of cast-iron. Where cast-iron pot sleepers are used, and double-headed rails are also used, the chair forms part of the same casting as the pot sleeper.

Thus, except in the case of the Barlow rail, we have, as essential parts of ordinary permanent way, rails and sleepers; and, where double-headed rails are used, we have also chairs.

I shall best bring before you the relative characteristics of the different forms of permanent way by describing in order the sleepers, chairs, rails, fish-plates, and fastenings; and by pointing out in each case the

mode in which each of the parts is applied in the construction of the different descriptions of permanent way to which I have alluded.

Beginning, then, with Sleepers. The materials that have been employed for sleepers are stone, wood, and iron. Stone sleepers, now very rarely seen, were much used in the early days of railways in this country, and possessed the great advantage of durability. They consisted of stone blocks measuring about 2 ft. square and 1 ft. thick, to which a cast-iron chair was attached by wooden trenails, driven into holes made in the stone. The blocks were placed about 3 ft. apart, from centre to centre, and they answered their purpose fairly well. The disadvantages attending them were, however, considerable. They were weighty and cumbrous, both to fix in the first instance and to move when the line required packing. The stone blocks also being unyielding, there was great difficulty in keeping the chairs firmly attached to them; and, there being an entire absence of anything to act as an elastic cushion between the wheels of the vehicles and the ballast, a road laid with stone blocks was harsh to travel over, particularly at high speeds. Some of these disadvantages might, no doubt, be lessened; and in places where wood and iron are expensive, and where, on the contrary, stone is cheap, and where the speed need not be high, the expediency of using stone sleepers should not be lost sight of.

It was thought at one time that permanent way could not be made too rigid, and a short length of railway was once laid with wrought-iron rails in chairs firmly bolted down on a bed of solid rock. The result, however, was that in a short time the rails, chairs, and fastenings were seriously damaged. The fact is, that the surface of the rails pressed by the wheels is exposed to extremely high

crushing strains; and, moreover, the parts of a railway and of the rolling stock are not made so mechanically accurate in shape nor so close fitting as to avoid a succession of more or less violent blows, which act on the parts of any permanent way laid on a rigid unyielding bed like the blows of a hammer on any material interposed between it and an anvil, and quickly destroy it. Experience seems to show that where wood is attainable, and is not exposed to special local drawbacks, it forms by far the most suitable material for sleepers.

Wood is used for sleepers in two ways-viz. as cross sleepers (Figs. 22 and 23, p. 58), and as longitudinal sleepers (Fig. 31, p. 76). The ordinary size of cross sleepers now used is 9 ft. long, 10 in. wide, and 5 in. thick; but these dimensions of width and thickness are exceeded on lines such as the Metropolitan and Metropolitan District Railways, on which the traffic is abnormally heavy. The wood usually employed in England and in Europe generally is Dantzic or Memel fir, but occasionally pitch pine and oak are used; and both of these-particularly the latter -are superior to fir; but the cost of them, as compared with that of fir, is generally too great to permit of their being extensively adopted. In other countries many descriptions of hard woods, such as teak, mahogany, and oak, are employed for sleepers, with the best results.

Sleepers should be of the soundest timber, with little or no sap, and they should be sawn true to form, at least at their lower side. Sometimes sleepers are allowed to be round at the top, and in this case a flat place has to be truly adzed or planed as a seating on which the chairs may firmly rest (as shown by the horizontal dotted line at the top of fig. 33). It is far better, however, that sleepers should be cut out of trees large enough to permit