538 OX DEAUGHT. 



keeps the traces constantly on the stretch, may frequently waste a power- 

 tul eflort without producing much efiect upon the carriaoe 



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 rehev^g the strain from the body horse, and reciprocally the 

 body horse from the leader ; so that these horses labour under all the dis- 

 advantages of a long, elastic, and constantly yielding connection with the 

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

 is variable, prevents the fuU and united effect, of their exertions beino- 

 properly communicated to the carriage. Tor, if a sHght obstacle, as a rul 

 or stone m a road, checks the progress of the vehicle, the shaft horse can 

 immediately throw his whole weight into the collar, and the united effect 

 ot his strength and impetus is conveyed unimpaired to the vehicle and 

 torces 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, beino- 

 lengthened into a continued and comparatively feeble pull, is insufficient ° 

 itwewish to destroy the impetus of a body moving ^vith violence we 

 receive It ^vlth a yielding resistance ; the action of catching a cricket-ball 

 exemphfies this perfectly; and, therefore, if the full effect of momenf am 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- 

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

 o± considerable importance when we arrive at the subject of wheel- 

 cari'iages. 



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

 the di^aught ought neither to be constantly uniform nor without remission 

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

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

 mjui^e the animal. 



Having determined upon the necessary quality of the resistance, wewiU 

 proceed to examme into the quantity or the degree of resistance or drauo-ht 

 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 poiver of traction he 

 ca7i exert, and the 7mmher of hours he can contimie to ivorh daily at that 

 speed ; and where there is no fixed condition which determines any one of 

 these, such as a particular load to be moved, or a certain velocity which it 

 IS desirable to attain, or a limited time to perform the work in, then the 

 object must be to search for those proportions of the three by' which at 

 the end of the day, the greatest quantity of work shall have been produced 



With respect to the first two, viz., the speed and power exerted, it will' 

 be obvious, that where a horse travels unloaded, the greatest distance he 

 can go in any given time for several days in succession without injurious 

 fatigue is the limit of his velocity : on the other hand, the load may be so 

 great that he can scarcely put it in motion— this is the limit of his power- 

 m both cases, the useful effect is nothing. But between these limits of 

 velocity and power, there is a proportion which affords the maximum quan- 

 tity of effect, and which, therefore, must be the most advantageous for the 

 apphcation of horse-power. 



It has been asserted by theorists, and the theory appears to be supported 

 by experience, that the velocity corresponding to this maximum, or that at 

 which a horse working continually a certain number of hours per day will 

 do the most work, is equal to half the extreme or limit of velocity of the 



