ROAD-MAKING. 



207 



mark generally understood " 'tween wind and water." If zinc cannot 

 be got of sufficient thickness, generally yellow-metal is employed, one- 

 sixteenth of an inch thick, which stands better than zinc; but it is. 

 much more expensive. Piling is generally driven by what is called the 

 " shears." 



When the span is too long for one beam, it is generally supposed that 

 what is called quarter-splicing and under-rodding is much stronger than 

 piers, for sometimes piers are apt to be damaged by floods. When there 

 is not a constant and steady weight on them, the spring of the timber 

 forbids this. 



SECTION 6. Stone-breaking Machines. 



In this section I merely wish to call the attention of landed pro- 

 prietors and their agents to an important machine lately introduced for 

 breaking stones. A large number of them are now at work, and are 

 giving very great satisfaction. The machine I refer to is " Blake's stone- 

 breaker," manufactured by Mr Marsden of Leeds. It is highly useful 

 for breaking ore for blast-furnaces, road-metal, and limestone. It can 

 be driven by steam, water, or horse power. 



Fig. 78 is a longitudinal section, and gives a side view of the several 



Fio. 78. 



parts of the machine. The circle G- shows the flywheel -shaft, and E 

 shows the position of the eccentric. A is the fixed jaw against which 

 the stones are pressed ; C is the movable frame or jaw, which works to 

 and fro, and presses the stones against the fixed jaw ; K is a bar of iron 

 which supports the jaw C, and acts as a pivot upon which C moves to 

 and fro. Inside there is an india-rubber spring which is pressed by the 

 moving jaw, and the spring of the india-rubber assists to throw the jaw 



