176 
Application of Steam Poioer 
or a circular motion, as the cutter of a revolvinfj digger. In 
separating the slice or spit, the wedge must necessarily compress 
and glaze it in some degree ; but the reacting pressure and 
sledging upon the sub-soil or whole ground of the under side of 
the share or cutter (so complained of in the horse-plough) maj' 
be altogether avoided in steam-power tillage. 
Thus, in the Woolston grubber, the downward pressure is sus- 
tained by the travelling wheels, which run upon the surface of the 
land ; in Mr. Fowler's balance-plough it is also borne by the 
wheels; in Mr. Halkett's ploughing apparatus it is carried by the 
wheels running along the guideway-rails ; and in rotary cultivators 
it is sustained by the axle in its bearings. So far there appears to 
be little difference between these modes of operating, as regards 
the amount of compression due to the cleavage of the wedge, — 
that is, the blade, share, or cutter used. And both traction and 
rotary cultivators may either "cut" the whole breadth of their 
work (as in paring) or save friction by leaving spaces between 
the shares, where the soil will In'eak up by its own rigidity. And 
both may employ tines of such a form as to tear the soil and 
draw out root-weeds, rather than cut them into short lengths. 
But, in the operation of raising and turning over the torn or 
sliced pieces, tlie revolving cutter that carries up a spit of earth 
(inverting its posture as it rises up), and then lets it fall, works 
with less expenditure of power than the plough-mouldboard, 
that prises and thrusts over a furrow-slice, with its screw surface 
hard rubbing all the time. 
The great mechanical advantage of the revolving steam-driven 
digger consists, however, in the almost direct action of the 
motive power upon the soil ; the engine actuates a drum (by 
the necessary gearing), and that drum does the cultivation — 
not hundreds of yards off, but there underneath it, passing shares 
through the soil as it rotates. What an economy of power 
compared with the traction system, in which the said drum, 
instead of carrying the tines or shares, has to pull a great length 
of rope, losing ])ower in the mere maintenance of a requisite 
tension, besides that consumed in the friction of pulleys and 
supporting rollers, or in trailing along the ground ; and the 
roj)e is not cultivating any more tlian the drum, but is a mere 
intermediate communicator of power to the distant machine 
which carries the tines or plough-shares. Then there would be 
a great saving of wear in working, as well as of time and labour 
in conveying from j)lace to place, when the macliinery is all com- 
prised in a single self-moving engine, having neither implements, 
ropes, anchorage, nor other detached parts to be set down, laid 
out, taken up, and transported ; and we must not forget another 
point of imj)ortance — that is the capability of the rotary digger 
