driven into a hole bored in the sleeper, and then the spike, which fits the hollow in the trenail very tightly, is driven into the trenail. This further compresses the wood of the trenail and drives the fibres of the trenail into the fibres of the sleeper.

For fastening the flat-bottomed rail on to the sleepers, spikes which are rectangular in cross section, and which have large projecting heads extending about

FIG. 51.

an inch over the upper surface of the foot of the rail (fig. 51), are often used. These rectangular spikes go by the name of 'dogs,' or 'dog spikes.' Wood screws (fig. 52) have been much used Dog. for holding down flat-bottomed rails. These are screws of iron, with large cutting threads on them, and act like ordinary joiners' screws. An objection to them exists from their being weak in the thread compared with the neck of the screw where it passes through the chair, and from the fact that the screw is dependent for holding strength on Wood the small quantity of wood included in the thread of the screw. The oxidisation of the screws is also apt to cause decay in the contiguous timber, and thus to make the screws become loose, in which state they are only equal to inferior spikes driven in decayed wood. Wood screws used in hard wood sleepers are not so open to the above objections.

FIG. 52.

screw.

Fang-bolts (fig. 53) are perhaps in this country the most satisfactory mode of fastening in ordinary use. Fang-bolts consist of bolts long enough to pass through the sleepers, with a screw cut on the lower end to fit a wide flat nut, having on it fangs or FIG. 53. Fang-bolt. short spikes, which imbed themselves in the lower side of the sleeper and prevent the nut from

A.Plan

of fang

turning round. When the head of the fang-bolt is turned round at the top, the bolt is screwed into the nut and draws the chair or rail firmly down on to the sleeper, and the elasticity of the wood of the sleeper keeps the bolt tight.

The drawbacks of fang-bolts are that after a time, and particularly in moist countries, the screw of the fang-bolt becomes set fast by rust and cannot be turned round. In many cases, particularly in tropical countries, the sleeper shrinks from the heat of the sun and so decreases in thickness, and it becomes necessary in consequence to tighten up the fang-bolts, but it is found that owing to rust the screw cannot be turned, and in the effort to do so the fang-bolt is broken. This has been found so serious a defect that in many hot countries the use of fang-bolts has been discontinued and resort has been had to the old-fashioned spike.

y

Section at

aty.z

A wedge spike (fig. 54) has been recently brought forward and seems to promise well. The spike is split, and the split receives a wedge which expands the two halves of the spike into the fibres of the timber of the sleeper, and causes the spike to assume with the wedge the shape of an iron dovetail which cannot be withdrawn, until the wedge has first been withdrawn. The mode of applying the wedge spike is to bore a hole through the sleeper and to insert below the sleeper an iron plate to hold up the wedge while the split spike is driven on to the wedge. The wedge can be withdrawn by a lever made for the purpose which grasps the bottom of the wedge and draws it as a dentist draws a tooth.

FIG. 54. Wedge spike.

The wedge or key by which the rail is held in the

chair has been already alluded to and shown in fig. 36, p. 84. The ordinary material for these keys is wood of hard description and good quality, which is generally compressed by hydraulic machinery until all moisture is driven out. When such a compressed key is driven into its position, it absorbs moisture from the air and expands, but in extremely dry weather wooden keys shrink and become loose in spite of the precaution of compressing them. Other descriptions of keys (such as wrought and cast iron keys) have been tried, but not with sufficient success to supplant the compressed wooden key. A wrought-iron key and a spiral key (fig. 55) are examples of these modifications.

FIG. 55. Spiral key.

A good key should hold the rail very firmly, but should at the same time be capable of being slackened when required. The compressed wooden key seems to fulfil these requirements better than any others, but, considering how extremely important it is that no movement should take place, a wooden key is at best an imperfect contrivance for the purpose of holding the rail firmly in its position.

There are many other details connected with permanent way which, if time permitted, I should have liked to discuss. But I have laid before you some of the main facts and principles connected with the subject. The time at my disposal does not allow of my describing the practical modes of laying the road, but I ought to refer to one part of the plate-layers' work, namely, the laying a line of rails round a curve.

The centrifugal force of a train passing round a curve tends to make the flanges of the wheels on the outside of the curve press against the rail on the outside of the curve with a force dependent on the speed,

the curvature of the railway, and the weight of the vehicle.

To counteract the effect of centrifugal force the outer rail is elevated above the inner rail (fig. 56), and the

FIG. 56. Super-elevation of rails on curves.

amount of super-elevation (which is the term generally employed) of the outer rail must be determined by the consideration of the maximum speed at which trains will pass round the curve. Thus the outer rails of curves near large stations, where all trains travel at a low speeds, require little super-elevation, compared with the same curves between stations, where the speeds may be high. The rule for super-elevation usually employed is expressed by the formula

W=Width of gauge in feet.

V=Velocity in miles per hour.

R=Radius of curve in feet.

E=Elevation of outer rail in inches.

On very sharp curves an extra rail is often laid on the inner side of the inner rail of the curve (fig. 57), with only

Plan

FIG. 57. Check rail on curve.

sufficient space left between the rails for the easy passage

of the flanges of the wheels. The extra rail, which is called a check rail, relieves the sideways pressure of the wheels against the outer rail, and prevents the wheels from mounting the outer rail.

The check rail, where the double-headed description of rail is used for the permanent way, is generally of the same section as the other rails, and is held in special chairs which hold both rails (fig. 58). Care should be taken that the distance-piece of the check rail chair be

Plan

Section

FIG. 58. Check rail with double headed rail.

tween the two rails should be kept low enough to allow the flanges of worn wheels travelling on worn rails to pass over it without striking it. Where flat-bottomed rails are used the check rail is often composed of a strong angle iron firmly bolted down to the sleepers (fig. 59). As an additional precaution against the wheels mounting over it, a check rail is frequently elevated about 1 in. above the adjoining rail on which the wheels run (see section in fig. 58).