where sulphurous and other acid gases are present in the atmosphere, the life of the rail is shortened to a material extent. On the whole, however, the balance of advantages is greatly in favour of steel.
Fig. 4, No. 5 (a), shows the section of a double-headed rail which has been in use for twenty years in the main line at a large station, and subsequently for five years in a siding, and one head of which is quite worn out This is, of course, an extreme case, but it very forcibly indicates the possible reduction of sectional area in a rail constructed of first-class material. On the other hand, Fig. 4, No. 6, shows the section of a rail which is no longer fit for the main line, but might still be used in a siding; in both these cases it will be observed that corrosion has more or less had the effect of reducing the portion of the rail not in contact with the wheels, and that the original shape of the head of the rail is no longer recognisable, so great is its reduction and deformation under the heavy percussive and abrading forces to which it has been subjected.
The improved form of permanent way actually in use upon the London and North-Western Railway at the present time is seen in Fig. 6. It consists of wooden sleepers, laid transversely, and which are of well-seasoned Baltic timber, into which creosote oil has been forced under pressure to the extent of 3¾ gallons to each sleeper. The sleeper, which is 9 feet in length, 10 inches wide, and 5 inches deep, when creosoted, weighs 150 to 160 lbs. To each sleeper two cast-iron chairs, each weighing 45 lbs., are secured by two iron spikes and two galvanised iron screws, a layer of hair felt being interposed between the sleeper and the chair. The spikes are cup-headed, slightly tapered, 6 inches
