828 VETEEINAEY HYGIENE 



this aspect of the subject has been alluded to in speaking 

 of the greatest muscular effort horses can exert. 



The angle of traction is the angle of inclination of the 

 traces, and much has been written on the most suitable 

 angle for different kinds of work. It would appear that 

 theoretically the angle is constantly altering depending 

 on the inclination of the road and its character, and 

 mechanisms have been introduced which are capable of 

 automatically altering the angle to suit various conditions. 

 In practice it is found that the traces should have a slight 

 inclination downwards, viz., from the horse to the carriage, 

 and this is true whether there be one or more horses 

 employed. If this is not effected the leader's efforts are 

 mainly expended in putting weight upon the back of the 

 wheelers instead of exerting it on the carriage. Whether 

 this is caused or not depends upon the type of harness 

 employed ; take for instance a tip-cart with a small horse 

 as leader, the traces of which are attached to the point of 

 the shafts ; in such a case the effort of the leader is mainly 

 expended in throwing weight on the back of the shaft 

 horse. This may be an advantage in going uphill, as it 

 artificially increases the body-weight of the shaft horse, 

 but is a great disadvantage on the level. It is considered 

 in a two-wheel cart, that the power of the horse is most 

 effective when not more than tz of the load rests on his 

 back. 



If roads were a dead level and frictionless (which is 

 impossible), a horizontal trace would effect its purpose, but 

 as in draught the weight has not only to be hauled but also 

 lifted over every obstruction, a trace at an angle is obviously 

 the correct mechanical system to adopt. 



There is a great loss of power caused by working horses 

 in pairs placed in front of each other ; the effective power 

 is not increased in the same ratio as the number of horses. 

 They are worked in this way mainly as the result of 

 convenience, as there must be some limit to the width of 

 a road. 



In agricultural operations advantage is taken of having 



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