to the Cultivation of the Land. 
189 
siderable stratum of earth, but being liable to jump out from 
below a mere film. Rotary forkers, too, thrusting- tines or 
spikes into the ground as they roll, experience a very different 
degree of difficulty in penetration to the revolving blades inde- 
pendently driven — in which the friction and pressure are on only 
one side or face of the blades. 
In Mr. Rickett's machine the tiller axis must be very near 
the surface of the ground, in order to avoid lifting the soil 
higher than is necessary ; hence it is placed as low as will 
allow room for the wheels, &c., for actuating it : but this 
arrangement involves the use of small motions, which cause 
excessive friction and wear. The machine exhibited at the 
Chester Meeting last year, and manufactured by the Castle Iron- 
works Company, consists of a locomotive engine with flue-and- 
tube boiler, 5 feet 3 in. long, mounted upon a framework, and 
travellirig on four carriage-wheels, the two main wheels being of 
4 feet diameter, with 12-inch broad tires, and the fore pair being 
used for steerage. It has double cylinders placed in the smoke- 
box, with the crank-shaft placed above the boiler, as in common 
portable engines ; and the propulsion forward is effected by 
means of reducing toothed gear-work engaging with cage teeth 
on the inside of one of the travelling wheels. An endless pitch- 
chain from a pinion on the end of the crank-shaft drives a wheel 
of double the diameter upon a shaft placed underneath and across 
the back of the machine. Behind this shaft, and parallel with it, 
the digger-shaft is hung in two radial links or arms, which allow 
it to be raised or lowered, motion being communicated from the 
main shaft by a couple of endless pitch-chains, one at each end, 
passing round pinions upon the two shafts. These pinions are 
only 5 inches in diameter ; while, to allow a depth of some 8 
inches, the circle described by the points of the cutters is about 
2 feet in diameter ; the pinions and chains having thus to bear a 
tremendous strain, which would be still more severe in case of 
the chains wearfng to unequal lengths ; and driving by pitch- 
chains is objectionable, because of the friction and wear. The 
digger-shaft is about 2j inches square, and about 7 feet long ; 
and the cutters, made two on a boss, opposite each other, are 
attached or removed by being slid along the shaft, the naves 
or bosses being so formed inside that they may be set in the 
right position for securing a helical arrangement of the cutters, 
in order that they may strike the ground successively, like the 
different pai'ts of a screw-blade. And the cutters are curved 
arms, carrying either 2T-inch prongs, or 5-inch wide, square-set, 
spud-shaped shares, of chilled cast-iron, or blades of an angular 
form, 7 inches broad, trucking each other, and so making two con- 
tinuous screw-threads or blades, each spiral wrapping once round. 
