414 ON DRAUGHT. 



An arrang-ement of this sort is, indeed, sometimes made use of, for raising 

 the earth from excavations, or the materials of a building ; but the exertion 

 is continued only for a few seconds, or for a distance of not more than ten 

 or twenty yards : if prolonged, the inconvenience would be seriously felt, 

 as it is, to a certain degree, in towing canal boats ; the length and curve of 

 the rope give an elasticity to the strain, and the necessity of keeping the 

 rope out of the water, or from dragging along the towing-path, compels the 

 animal to keep up a constant, unremitted pull, and that, too, in an oblique 

 direction, so as to throw him into an unfavourable position. We accord- 

 ingly find that, under these circumstances, the average work of a horse is 

 equivalent only to about four-fifths of that given by Smeaton, Desaguil- 

 liers, and others, who estimated the power of the horse from the work done 

 in a horse-mill, where the resistance is inelastic, and all circumstances 

 favourable, with the exception of the circular path. 



The disadvantage of this kind of resistance is well known to carmen, 

 though of course without consideration of the reason. A horse is said to 

 pull better when he is close to his work, that is to say, when he is attached 

 at once to the body to be moved, because every exertion he makes is 

 then communicated at once to the mass ; but the leader of a team, unless 

 he keeps the traces constantly on the stretch, may freque^itly waste a 

 powerful effort without producing much effect upon the carriage. 



Another inconvenience resulting from harnessing horses in a team, or 

 one before the other, is, that the leader, by tightening the traces, is con- 

 tinually relieving the strain from the body horse, and reciprocally the body 

 horse from the leader ; so that these horses labour under all the disadvantages 

 of a long, elastic, and constantly yielding connexion with the load, which 

 is not only fatiguing to them, but, in cases where the resistance is variable, 

 prevents the fiill and united effect of their exertions being properly com- 

 municated to the carriage. For, if a slight obstacle, as a rut or stone in 

 a road, checks the progress of the vehicle, the shaft-horse can immediately 

 throw his whole weight into the collar, and the united effect of his strength 

 and impetus is conveyed unimpaired to the vehicle, and forces it over the 

 obstacle ; but if any elasticity is interposed between the power and the 

 resistance, as in the case of the traces of the leader of a team, the whole, 

 or the greater part of the effect of impetus is lost, and that force, which, if 

 concentrated in one effort, would effect the object, being lengthened into 

 a continued and comparatively feeble pull, is insufficient. 



If we wish to destroy the impetus of a body moving with violence, we 

 receive it with a yielding resistance; the action of catching a cricket-ball 

 exemplifies this perfectly ; and therefore, if the full effect of momentum is 

 wanted, all elasticity in the direction of the movement should be avoided. 



We have entered rather fully into the consideration of this particular 

 point, because the principle is not only applicable to the mode of commu- 

 nicating the immediate action of the moving power, but will be found also 

 of considerable importance when we arrive at the subject of wheel-carriages. 



A consideration of these various points brings us to this conclusion, that 

 the draught ought neither to be constantly uniform or without remission, 

 nor yet yielding or elastic : sudden shocks or violent changes in the velocity 

 must also evidently be disadvantageous, as tending to distress and injure 

 the animal. 



Having determined upon the necessary quality of the resistance, we will 

 proceed to examine into the quantity or the degree of resistance or draught, 

 and the speed best adapted to the exertion of the animal. The useful effect 

 of a horse, or the work done, must evidently depend upon three things, viz, 

 the rate at which he is made to travel, the power of traction he can exert, 



