Page:The Canal System of England.djvu/56

 part on blocks of concrete, weighing 220 lbs. each in the case of heavier principal rail, and half this for the other rail. This arrangement cost £50 to £80 more per mile than the arrangement with sleepers, but proved less expensive to maintain. A steel rack, bolted to the web of this principal rail, provided the resistance necessary for haulage, the weight of the locomotive used being insufficient to give this by adhesion.

Though no wharf actually existed on the length of canal used for experiment, the arrangements necessary, had such wharf existed, were fully tested. At one point the line of rails was raised to a height of 9 ft. 6 in. above the level of the tow-path, being carried on posts and brackets; this elevated portion being connected with the level line on each side of it by gradients of 1 in 8. The carrying posts were 12 in. in diameter, and were spaced at 18 ft. 8in. centres. A cap piece 8in. by 10 in. in section spanned the gap between consecutive posts. The principal rail was laid directly on this cap piece, whilst the other was carried by a stringer, supported at each post on brackets.

The conductor for the current was supported on pine posts, 23ft. long, spaced at 35 to 44 yards apart. It consisted of 8 millimetre wire, carried by porcelain insulators. The potential used was 500 volts and the principal rail served as conductor for the return current. The source of power was a 15-horse-power portable engine, driving a 9-kilowatt dynamo, and a large storage battery was also