402 



SCIENCE OF AGRICULTURE. Tart II. 



must have a natural drainage, by lying in one even slope or slopes ; it must be in pasture ; 

 and the soil must be of uniform consistency, and free from stones. Rut even where 

 these favourable circumstances combine, we think two swing ploughs, with finless shares, 



following in the same track, would effect the same object sufficiently well for all agricul- 

 tural purposes; and for drains in ornamental grounds, no machine will ever equal 

 manual labour. 



2646. The Duke of Bridge waters draining plough {Jig. 321.) is used for making open 

 drains of a small size (c), regular shape, and from live to nine inches deep. The 



share fa) has a coulter (6) fixed to it, projecting upwards, to cut one side of the drain, 

 and another coulter d) fixed to the beam and also to the share at its lowest end. The 

 turf which is tints cut out passes between the coulter (<-/) and the mould-board {e), and 

 is thus lifted clearly out of the trench. The depth of the drain is regulated by the wheels 

 at the fore end of the beam (/). This plough is drawn by four or six horses. 



*2647. Various draining Roughs have been invented and tried by Arbutlmot, Makie, 

 M'Dougal, Green, Pearson, and others. Pearson's will be afterwards figured and described. 

 2648. The pressing plough is properly a roller, and will be found noticed among 

 machines of that class. 



*2649. The only essential plough to be selected from these three sections is the improved 

 Scotch swing plough, with or without one or two wheels, according to circumstances ; 

 and with the mould-board, share, and coulter, set to suit different soils, as flinty, chalky, 

 &c. ; or soils in different states of culture, as old turf, heath, steep banks, ley, &c. 



Subsect. 3. Tillage Implements, known as Scarifiers, ScuJJlers, Cultivators, and Grubbers. 



2650. The use of pronged implements, as substitutes for the plough, is of comparatively 

 recent date. They differ from the plough in stirring the soil without reversing its 

 surface or altering its form, unless, indeed, they in some cases tend to even or level 

 inequalities ; they act both as the plough and harrow at the same time, and on suitable 

 soils, and at proper seasons, much more labour is effected with less expense of men and 

 cattle. Wherever, therefore, lands require to be stirred for any purpose except that of 

 reversing the surface, or laying them into beds or ridges, recourse may be had to pronged 

 tillage implements, such as we are about to describe. 



2/> "'1. In estimating the value of pronged tillage implements, General Beatson ( New System of Cultivation, 

 1820) applies the principle of lessening"power and employing time. He says, if we applv the principle of 

 petty operations to any stiff land, by taking that depth of furrow which can easily be ploughed with two 

 horses, and repeat the operation (or plough the land a second time), we shall arrive at the end proposed, 

 that is, the same depth of ploughing, with absolutely less exertion of animal strength than if we were to 

 plough the same depth with four horses at one operation. 



2652 This may be illustrated by supposing the resistances to the plough to be in proportion to the 

 squares of the depth of the land. If so, and we are to plough at once witli four horses, six inches deep, 

 the resistance at that depth would be 6 x 6 = 36 : but if with the same four horses, using two at a time, 

 we plough the same depth of six inches at two operations, taking only three inches at' each, then the 

 square of the first depth is 9, and the square of the second, 9 ; making 18 for the total resistance, or the 

 power expended by the two horses, in ploughing six inches deep, at two operations. 



'JiijJ. A farther illustration may be made by supposing the same four horses, which had ploughed at 

 once six inches deep, and had overcome the resistance of 6' x 6 = 3fi, applied, separately, to four light 

 ploughs, or other implements, and to plough only 1| inch deep at a time, and to go over 'the same land 

 four times. In this case the sum of all the resistances to be overcome, or the animal force expended, in 

 these repeated ploughings, would be no more than 9 instead of 36 ; because the square of I± = 2£, which, 

 multiplied by the four ploughings, gives 9, or only one fourth of the power expended in ploughing at once 

 six inches deep. Hence it appears, that in ploughing six inches deep, with four horses, each horse exerts 

 a force = 9 ; whereas in taking only ]| inch deep, the force he exerts is not more than 2j. 



2654. Farther, supposing that a horse exerts, in drawing a plough, a force of 160 pounds, it is evident, 

 if four horses are ploughing six inches deep, the total force exerted will be o40 pounds, or 160 pounds by 

 each ; but if they be required to plough one inch and a half deep at a time, then the total force expended 

 by the four horses will be only 160 pounds, or 40 pounds by each horse. 



2635. Application. This leads General 8. to the principle on which his small scarifiers are constructed. 

 '* They have," he says, " four hoe-tines in the hind bar, and I will suppose that there are four harrow- 

 lines ^instead of three) in the front liar, so that each scarifier may be considered as four small ploughs, 

 with four shares and four coulters. If we suppose one horse attached to this implement, and that the 

 force he exerts is 160 pounds, it is obvious that in scarifying to the depth of one inch and a half, he will 

 exert these ItiO pounds upon the four pairs of tines, or a force of 40 pounds upon each pair. But, in fact, 

 the force required to draw the scarifier will be considerably less than to draw any form of plough, because 

 the hoe, or share-tines, being much thinner and sharper than a ploughshare and mould-board, will of 

 course meet with much less resistance in stirring the sou." General B. goes on to relate some experiments 

 by winch he considers he has " clearly proved that the least expensive method of preparing the land for 

 wheat, after tares, beans, peas, or clover, is simply by using the scarifiers." This we conceive is carrying 



