of timber. The upper outer edges of the baulks were beveled at 45 degrees, and the rails fixed to the bevel surfaces so as to be angled out at the same inclination. The rails, baulks and track beam were fastened together with single bolts passing clear through. The gauge of the load-bearing rails was 22.5 inches (57 cm) between the outer edges. The support girders were not stayed, either. The track beams were interrupted by short posts 42 inches (107 cm) high and sitting on the support girders, and bearing the central traction rail (also referred to as the upper track beam) which was a girder 17.5 inches (44.5 cm) thick. This thickness included iron straps, replaceable when worn, which were fixed along the sides so as to leave a slot along the bottom of each side. The flanges of the horizontal gripper wheels fitted into these slots. The support posts were supplemented by diagonal trusses, as seen in photos of the experimental line. The experimental line did not feature junction arrangements, so these only appear in print. A swing bridge arrangement was envisaged: A junction switch is formed of a single swinging section, turning upon a hinge of great strength attached to one of the pillars. A movement of four or five feet (1.2 to 1.5 metres) by the free end of the switch was enough to permit the cars and trucks on one track to clear the end of the other track. The free end travels upon a carriage provided with rollers, moving upon a supporting rail. Suitable mechanism is provided for operating the switch and locking it in place. The switch would have had to be operated manually, somehow. Neither the experimental line nor published illustrations gave any indications as to how routine inspection and maintenance of the permanent way were to have been carried out, without recourse to ladders or scaffolding erected in the street below. Wheel system Each item of rolling stock had two trucks or bogies, with four flanged load-bearing wheels each. The major peculiarity of the latter was that they were not vertical, but angled inwards: Each truck consists of a horizontal rectangular wrought iron frame, stiffened by cast iron pieces and provided with stiff pedestals bolted to its under side, in which were fixed short axles for the wheels. Each truck had four wheels set at an angle of about 45 degrees,