A floor that sags or springs considerably under moving loads may be made much stiffer by taking up a couple of floor boards every 6 feet in the length of the floor and fitting slightly wedge-shaped blocks between the beams, in a continuous line, as shown in Fig. 56. The blocks should be made of 3-inch plank, of the full depth of the floor joist, and cut so that the grain of the wood will be at right angles to the joist, that they may not become loose as the wood shrinks. Before putting the blocks in place holes should be bored through the centres of the beams and a 1¼--inch rod passed through all the beams, the rod having a head at one end and a nut on the other. After the rod is in the blocks should be fitted closely in place and the nut then screwed up until the floor becomes crowned, owing to the shape of the blocks. A floor crowned in this way acts like a truss, and will be much stiffer under a moving load than when simply bridged in the ordinary way, although the strength of the floor, to support a distributed load, such as grain or large boxes of merchandise, is in no way increased. If the floor and ceiling must be kept perfectly level the top of the beams will, of course, either have to be dressed off or the floor furred to a level, and the ceiling will also have to be furred.