34 BRITISH HUSBANDRY. [Ch. Ill, 



the horses' shoulders, thus being contrary to the correct principles of draught, 

 wliich require tliat wlien the muscular exertion of an animal is necessary 

 in drawing a load over rough ground, it should be in an inclined direction 

 from the jioint of draught upwards to the shoulder. It lias no doubt, how- 

 ever, been originally formed in this manner for the convenience of mounting 

 a box upon it for the carriage of any rubbish that may be picked off grass- 

 land, as well as for adding to the weight wliere that may be tliought neces- 

 sarv, or for placing a seat upon it for the driver. To the collection of rub- 

 bish when grass is to be rolled, there can be no objection ; nor much to the 

 indulgence of the driver with a seat; but, if merely intended for the increase 

 of weight, the object may be more effectually answered by lianging it to the 

 axle withinside of the hollow cylinder hereafter described : for, if placed upon 

 the frame, it adds more to the draught than in the latter manner, without 

 equally increasing the pressure upon the land ; as the weight rests upon the 

 gudgeons of the axle, in consequence of which the friction is for greater 

 than in rollers of equal weight, if constructed upon proper principles. The 

 mode of mounting them, as delineated in the frame of the convex roller, 

 hereafter described, is therefore preferable. 



In some cases, indeed, the horses' traces are applied directly to the axle 

 without any frame, in the manner depicted in the description of the con- 

 cave roller : this saves expense, but the instrument is less true in its revo- 

 lutions, and is therefore subject to drag in a manner which may be injurious 

 to grass, or to seeds which require rolling. 



, A very general notion prevails among farmers, that rollers of equal 

 ■weight are more effectual when made long than short : it is, therefore, 

 not unusual to see the diameter of the cylinder lessened, so as to bring 

 them to the same-weight, though made of greater length ; in the idea that, 

 as they will thus go over a greater extent of ground in the same time, 

 more work will be equally well performed. In this, however, there is a 

 double error: first, because the same weight, resting upon a greater length 

 of g^round, has more points to sustain it, and therefore the weight which 

 presses upon each is lessened ; wherefore, although more ground will be 

 gone over, yet the work upon it will be less effectually j)erformed ; secondly, 

 by lessening the diameter of the cylinder, the power requisite for draught 

 is increased ; for it has been proved that the same strength which is re- 

 quired to draw a roller of iialf a ton weight over a height of two inches, 

 when the diameter is one foot, will suffice to draw rollers of 1.5 and 18^ 

 cwt. when their diameters are respectively two and three feet*. If, how- 

 ever, the weights of the respective instruments be equal, that of the smallest 

 diameter will make the deepest impression upon the ground ; but, on 

 lieavy arable land, it will be more subject to drag the soil before it. It 

 follows, therefore, that large rollers are so much more easily drawn, that 

 their weight may be increased to an extent sufficient to counterbalance any 

 probable advantage in efficiency which may be possessed by those of 

 smaller diameter. 



HOLLOW ROLLERS. 



This increase of diameter — were the cylinder solid — would, however, ne- 

 cessarily occasion either too great an increase of weight, or else too great 

 a diminution of length; to avoid which holloiv iron rollers are much em- 

 ployed upon gentlemen's parks and other grass-lands in which it is import- 

 ant to preserve great smoothness of surface. They also possess the advan- 

 tage of allowing their heaviness to be increased, when necessary, by hanging 



* Quart. Joiirn. of Agric. N. S. vol. i. p. 705, 



