is necessary to call an engine cautiously past a signal at "danger," and which are termed "calling on arms."
On an average the fitting shop at Crewe turns out about nine signals per week, including composite or bracket and gantry posts, some of which have been constructed to carry as many as twenty-four signal arms.
On the other side of the shop are arranged a number of erecting frames, on which the interlocking apparatus is built up. The frame used by the Company is known as lever actuation, with horizontal and vertical bar locking. The horizontal bars are of Bessemer steel, rolled to a shallow channel section, the locking studs being squared to fit the channel and secured by riveting. The vertical bars are also of steel, notched, the notches being punched out cold. Each vertical bar is guided by a channel the length of itself, one wall of which is made deeper than the other; notches are cast in this to act as guides for the horizontal bars, these notches being faced by a special drifting machine at the rate of thirty-five notches per hour. The apparatus is characterised by great strength and simplicity, and, an unusual amount of special machine work being employed in its construction, a perfect interchangeability of parts is secured which is highly essential to economical maintenance. This is sufficiently demonstrated by the fact that, since the introduction of the present form of apparatus and methods of construction, the annual cost of maintenance has been largely reduced.
Signals are worked from the signal cabins by wires, but the points are actuated by rods. Trailing points are worked at a distance of 220 yards from the cabin, but in the case of facing points the distance is restricted by the Board of Trade to 150 yards, increased
