CH. X RIGID OR ELASTIC CONNECTIONS 1 85 



The relation of the power of a horse to the draught 

 of a vehicle is modified by the condition of the 

 road, since the exertion of moving his own body is 

 much the same to the horse, whether the surface of 

 the road is good or bad, provided it is not slippery 

 or so loose and deep as to yield excessively to 

 his feet ; but as the surface of the road deterio- 

 rates, more power is required to pull the same 

 vehicle. 



There is some difference of opinion as to the 

 relative merits of a rigid, and an elastic connec- 

 tion between the horse and the vehicle ; since the 

 animal's motion forward is not uniform, but, as 

 shown by the experiments of Marey and others, 

 consists of a series of motions of varying velocity, 

 a number of shocks must occur with a rigid con- 

 nection which are avoided by a certain amount of 

 elasticity. 



As has been remarked, when speaking of carriages 

 with and without perches, the springs to some extent 

 take up such shocks, and a number of devices are in 

 use, such as the spring swingle-tree of a brougham, 

 or a dog-cart and the spiral springs connected with 

 the traces sometimes used with heavy business- 

 vehicles. With a spring interposed, a forward 



distance through which it acts and not by the amount of the pressure 

 alone. 



As the load becomes greater and the inclination of the legs of the 

 horse must be increased to move it, the strain on them will be in- 

 creased to their injury. 



