15 



In going down steep hills the machine 

 may be held back by a horse ridden behind, 

 and hooked on by the South American 

 surcingle and single trace ; or the machine 

 may be very conveniently blocked by 

 lashing a bar of wood across the shafts, 

 close in front of the wheels, and taking out 

 the screw which fastens the shafts to the 

 axle. The horse will then bear back 

 against the wheels instead of against the 

 axle, and the friction against the wheels 

 will increase or decrease directly as the 

 downward impetus. 



The principle of locking two-wheeled 

 carriages by creating friction on the wheels 

 induces a slight downward pressure on 

 the horse's back. But the long shafts act 

 as a lever in the horse's favour, and the 

 extra pressure on his back is not to be 

 spoken of in comparison with the labour 

 of bearing back a loaded cart. 



