to the Cultivation of the Land. 
179 
advancing, thus propelling it, the spur-wheel on the carriage-wheel 
axle regulating the rate of advance. This principle of action 
is the chief source of economy in power in driving a rotary 
tiller : the shares encounter resistance to their passage through 
the ground, and, b}' moving them in the right direction, you 
may take advantage of this reaction, and, while applying the 
whole of the motive power almost directly to the digging-shaft, 
have the machine moved onward without any separate assistance 
from the engine, simply in consequence of the direction in which 
the cutters move. If three shares at a time be constantly passing 
through the ground in a backward direction, with a force (or 
draft) of say 6 cwt., the machine is urged forward with a force 
equal to 6 cwt., or the draft of three horses — sufficient for its 
propulsion at the very slow pace i-equired. And in this way 
Mr. Usher completely overcame the objection as to " waste 
of power " in transporting the engine over the land. The first 
machine was built by Mr. Slight, engineer, of Leith Walk, Edin- 
burgh, and was tried in w"ork during the latter part of the year 
1851 and the spring of 1852. The engine was of 10-horse 
power, and the weight about 6? tons ; and it is certain that the 
propelling action of the rotating tillers not only enabled it to 
mount inclinations which it could not cope with by the mere 
adhesion of the broad roller upon which it travelled, but that no 
part of the motive power was engaged in effecting the onward 
motion. Indeed, it was considered at the time that the thrust of 
the slowly-moving shares was more than sufficient for the propul- 
sion of the machine. For in some of the experiments, when the 
land had been dug up for the first time, the machine was imme- 
diately taken over it again, working as easily as at first ; and 
6 J tons, riding upon a wide roller (not of large diameter) and a 
pair of wheels, across soft freshly-moved earth, at a pace of 3 
miles an hour, evidently required the full power of the engine, 
while a breadth of 4 feet 2 inches was" being ploughed up deeply 
at the same time. 
Mr. Usher having made several important improvements, 
again tested the machine at Niddry Mains, near Edinburgh, in 
February, 1852. 
" The soil is left in a broken condition, as by the fork or spade, and arrange- 
ments exist by which tlie three operations of manuring the soil, sowing, and 
covering in the seed, are done at the same time. It travels at the rate of three 
miles an hour, e(iual to 9 acres a day, or, allowing for turning, stoppage, &c., 
say 7 acres, which it has done in its various trials, for an expenditure (working 
expenses) of 17s. Gf^., or 2*'. per acre. It travels well on common roads" 
ascending acclivities of one in ten, and turning round in a circle of IG feet 
diameter, and is adapted for any other purpose to which steam-power is 
applied." — Professor John Wilson, at the Koyal Institution, February 25, 1853. 
In the spring of 1855, another machine was completed, having 
N 2 
