Thinking of the rules of cricket where it says that the side that are in play until they are all out while the side that were all out are all in again... This is an extract from the official report by Inspector Captain H.W. Tyler for the board of Trade about an accident at London Bridge on 29th January 1854. "The passenger trains between London and Greenwich, run every quarter of an hour, in each direction; during the day, the same engine that brings the up train from Greenwich, taking the down train from London. At London Bridge station, the platform is situated between the up and down lines, which converge, at a short distance from the station, into one line, and this one line is traversed by both the up and the down trains, for a short distance. In order to transfer the up train engine to the down train, the up train is detached from its engine at about 360 yards from the points at which the two lines meet - and whilst proceeding at a sufficient speed, to admit of the engines getting forty or fifty yards ahead of the train, before arriving at the points, and then being turned on to the down train - the up train is, by a subsequent movement of the points, caused to run up the other side of the platform. Alternate trains are started from different sides of the platform. As soon as the up train has arrived, and discharged its passengers, it becomes the down train for the next trip. The up engines and up trains must, consequently, be turned by the pointsman, each in different directions, on alternate trips; that is to say, in the cases of the hour and half hour trains, the engine goes in to the north of the platform, whilst the train goes to the south; and, in the cases of the quarter and three quarter trains, the engine goes to the south of the platform, and the train to the north."