ENGINEER HORSES. 91 



to support the centre of gravity, and keep the 

 body steady ; and as long as the one side of the 

 ground continues higher than the other, the track 

 continues bending towards the low side. If the 

 ground again becomes level, the path, if not 

 counteracted by observation and design, goes on 

 in the last direction of the body, how different 

 soever that may be to the direction of the path on 

 former level ground ; and if the ground begins to 

 slope the other way, a bend in the other direction 

 takes place, unless where observation prevents it. 

 Any one who looks at foot-paths, not designedly 

 made, even when they lead across the common 

 from one well known and often frequented spot to 

 another, will see that they are made a good deal 

 upon those mechanical principles, and not only so, 

 but when there is, upon ground having side slopes, 

 a beaten track on the grass by the side of a per- 

 fectly straight artificial walk, the effects of this 

 natural balancing of the body may be seen. It 

 does not require hills to produce them, for the 

 ground immediately at the sides of the track may 

 be perfectly level, and yet the track as much 

 twisted as if every little swell extended onward and 

 rose to a great mountain. A slope forwards or 

 backwards does not produce similar effects ; but 

 when there is an increase, and at the same time a 

 twist in the ascending slope, the natural paths of 

 men, and even of large quadrupeds, have gene- 

 rally twists there, and twists which are very dan- 

 gerous for wheeled carriages in moving rapidly. In 

 the early ages of English history, men and horse- 

 men, and pack-horses, appear to have been the 

 only engineers in road making; and as, in a horse 

 with a rider or a load, the centre of gravity is 



