ENGINEER HORSES. 103 



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 great 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 perfectly 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 generally 

 twists there, and twists which are very dangerous 

 for wheeled carriages in moving rapidly. In the 

 early ages of Englfsh history, men and horsemen, 

 and 'pack-horses, appear to have been the only en- 

 gineers in road making ; and as, in a horse with a 

 rider or a load, the centre of gravity is higher, and 

 consequently swings more than in an unloaded 

 horse, those twists at the double curvature of the 

 steep hill occur in many places where the old line 

 has been preserved, and among other places, just 

 near the top of Highgate Hill ; and it is a fact, that 

 though those twists are dangerous for carriages, they 

 are easier for those who walk, or ride slowly, than 

 if the road went straight up. 



Any one may convince himself of the truth of 

 these effects of the centre of gravity by trying to 

 run in a horizontal direction round a hill, without 

 getting farther from the summit or centre of the 

 hill ; or how difficult it is to rim round on the slope 

 of a circular basin or hollow without getting nearer 

 to its centre or bottom. If the battlements of a 



