Page:Whymper - Scrambles amongst the Alps.djvu/77

Rh with two pairs of horizontal driving-wheels as well as with the ordinary coupled vertical ones, and the power of the machine is thus enormously increased; the horizontal wheels gripping the centre rail with great tenacity by being brought together, and being almost incapable of slipping, like the ordinary wheels when on even a moderate gradient.

The third rail is the ordinary double-headed rail, and is laid horizontally; it is bolted down to wrought iron chairs, three feet apart, which are fixed by common coach-screws to a longitudinal sleeper, laid upon the usual transverse ones: the sleepers are attached to each other by fang-bolts. The dimensions of the different parts will be seen by reference to the annexed cross section:—

Let us now take a run on the railway, starting from St. Michel. For some distance from that place the gradients are not of an