The line follows a northerly course after leaving the southern terminus, and roughly clings to the bank of the river so far as Chiromo. Here it swings across the waterway over a bridge about 420 feet in length, to gain the valley of the Ruo River. This bridge is the outstanding feature of the railway, on account of its interesting lifting span, which is of novel and unusual design. When the railway was plotted the Government stipulated that there should be no interference with navigation on the river, although the waterway, as a highway of traffic, has fallen practically into desuetude since the railway was constructed. However, official requirements had to be met, and these demanded an opening 100 feet wide, and giving a clearance of 30 feet in height at high water. The ordinary type of draw or swing bridge, to satisfy this requisition, was quite out of the question, because the need to open the bridge is very rarely experienced, and when the demand does arise, the time occupied in the operation is of minor importance. Heavy expenditure under this heading, therefore, was not justifiable.
THE BASCULES BEING LOWERED BY CABLES AND WINCHES FROM EITHER CLIFF-FACE
[See [page 302]
THE BASCULES LOWERED, SHOWING THE FRENCH ENGINEERS AT CENTRE MAKING THE CONNECTION
ERECTING THE BASCULES FOR THE FAUX-NAMITI BRIDGE ON THE YUNNAN RAILWAY
Moreover, as native labour was to superintend the work of opening and closing the bridge, the simplest arrangement possible was essential, and, furthermore, had to be capable of hand manipulation. The designing engineers, Sir Douglas Fox & Partners, and Sir Charles Metcalfe, Bart., evolved an ingenious solution. On the top of two adjacent piers carrying the span in its normal position, a tower was erected on either side of the opening, with two simple, single, vertical racks on either tower. At the top of each tower a platform extending the width of the bridge was provided, together with a large sprocket wheel at either end. A chain passed over each sprocket wheel, one end being attached to a corner of the bridge, and the other to a heavy counterweight.
To open the bridge, all that the natives have to do is to wind a winch which rotates the sprocket wheel, and as the counterweight descends the whole span rises vertically and horizontally, being guided in its movement by the rack on each tower. The counterweight is the full width of the bridge, and when the span has been lifted to its fullest extent the counterbalance weight lies across the track, to form a high barrier to any one attempting to cross the bridge when the span is open.
It will be seen that the bridge acts on the principle of a sash window, where the sash weight counterbalances the weight of the moving portion, and in lifting only the friction of the moving parts has to be overcome. To guard against disaster from tampering or misuse, the bridge, when either raised or lowered, is locked. To lower the bridge it is only necessary to reverse the winding direction of the winch. The span of steel moved in this manner weighs 55 tons, and the whole operation of opening and closing occupies about half-an-hour, eight men under a native superintendent sufficing for the movement of the winches. It is an unusual type of lifting bridge, but it is doubtful whether a simpler and cheaper means of meeting the situation could have been devised, while the maintenance expenses—a vital consideration in such a remote country—are reduced to insignificance.