18) Now here are the men in the control tower. This, by the way, is at Toton, near Nottingham, but the principle is exactly the same. On the desk are lines which correspond to the tracks; and the buttons, which have a sort of miniature signpost on them, are turned round to move the points at the entrance to the yard. The older man is holding a microphone in his hand by which he can speak through loud speakers to the men on duty outside in the marshalling yard.

You’ve already seen quite a good deal about railway working. But I wonder if you realise that everything you have already seen would come to a complete standstill without power...