This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol1", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
Fig. 272A shows Morton's " Valtor" spring floor. This floor is supported upon girders which rest upon cast-iron supports, which in turn are supported upon stout springs. The object of the springs is to impart elasticity to the floor when it is being danced upon. When the floor is not required for dancing purposes wedges may be driven between the girders and the supports so as to make the floor firm as an ordinary floor.
The best method of laying floor boards is to lay six or more loosely across the joists and cramp them up tightly with a cramp (such as that shown in Fig. 273) when they are nailed. A few more boards are then laid, cramped, and nailed; and so on until the floor is complete.
A method of laying floors sometimes used is that known as "Laid folding." In this method about six boards are placed across the joists with their edges as close as possible; one of the outside boards is nailed and the position of the other outer board is marked upon the joists, the four intermediate boards are taken up and the outer board nailed a little closer to the one first fixed. The intermediate boards are then relaid in the form of an arch between the two outer fixed boards, and a stout board is laid transversely across them upon which a workman jumps, thus forcing the intermediate boards flat against the joists below in which position they are nailed. A few more boards are treated in the same manner, and the operation repeated until the floor is complete.