1042

THEORY AND PRACTICE OF ENGINEERING.

B OOK 11.

falling draws it down, and being compressed in the tub, without any other means ofescape, it rushes with violence through the pipe D : within the tub is a small stool H, onwhich the air falling, more easily escapes from the water, which runs away by a trough,always kept full, so that the air may not issue with it. A wheel driven by a streamis shown at KQ on the plan : the hammer weighs about 300 lbs., and is stopped or set inmotion by means of a sluice at Q.

Forge Hammers are still used at many of the iron-works on the continent, which receivetheir motion from a water-wheel, as shown at the side of the preceding figure, and atLanslebourg in Sa-voy, in a manufactoryof iron hoes, the forgeis blown by meansof water descendingthrough two pipesinto a trunk, as de-scribed above.

The wipers whichlift the cogs or cams ofthese forge hammershave their acting forceson the involutes of acircle, whose radius isthat of the wheel, uponwhich they are fixed,and they elevate thehammer by acting

upon a surface perpendicular to the vertical direction in which it rises, and a uniformmotion is obtained.

Block Machinery at Portsmouth, put up by Mr. Maudslay in 1802, after designs ofMr. Mark Isambard Brunei, commenced working in 1804. This very complete and per-fect system of machinery for the manufacture of every part of ship blocks consists of44 separate machines, which operate upon 200 varieties required for the tackling of thenavy, together forming the finest example of practical machinery in the world: the 44machines consist of 21 varieties, which form three sets of blocks of different sizes at onetime. The building that contains them has a steam-engine of 32 horse-power in themiddle; it is connected on one side with seven large machines for sawing the timber intothe proper sizes for the blocks, and on the other with the thirty-seven block-makingmachines.

Fig. 1600.

FORGE HAMMER.

Fig. 1601.

SAW MILL OF THE PORTSMOUTH BLOCK MACHINERY.

The tree is first brought to the straight-cross cutting saw ; secondly, submitted to thecircular-cross cutting saw; thirdly, to the reciprocating ripping saw, which cuts the elmin the direction of the grain of the wood, and afterwards in a contrary direction ; fourthly,to the circular ripping saw, and the several parallelopipedons into which the timber hasbeen sawn are then taken, fifthly, to the boring machines, where they are fixed in a frame,and two centre bits are applied; one bores a hole for the centre pin, and the other, perpen-