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Show 102 DIRECTION OF THE TRACK. footpaths, if there is nothing to confine them to a particular direction. So that the formatiOn of the path is not a matter of reasoning and judgment at all, but purely mechanical. When an animal, however sm_all or large, walks, it must always so move ?-S that 1ts centre of gravity is supported, otherwise 1t w~mld fall. Now that is obtained partly by the motwns of the legs, and partly by those of the upper portions of the body. The more legs there are, the ?entre of gravity has the more props, and ~o there 1s less need for counterbalancing motions m the body above. Ants have six legs, quadrupeds four, and man only two ; so that man needs more \ exertion of his body to balance himself than the quadruped, and the quadruped more than the ant. The man too is upright, and even the quadruped is higher in proportion to its breadth than the ant. Thus .the centre. of gravit:y swing~ by the longest lever m the man m proportiOn to his whole weight and by the shortest in the insect ; and thus the m a~ is more affected by the position of the surface on which .he walks than t~e quadruped ; and the quadruped 1s more affected m that way than the insect. yY"here the g~ound is p:rfectly level, the man's path IS nearly straight; but 1f the ground rises to the one hand, the path always takes a twist to the other because the foot which is on the high ground throw~ the c~ntre of gravity the other way, and the other foot 1s advanced towards the low side, in order to support the centre of gravity, and keep the body stea~y; an~ as long as the one side of the gr0!:ad contmues higher than the other, the track continues bending towards the low side. If the ground again becom.es 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, ~ bend in the other direction takes place, ooless where ENGINEER HORSES. 103 observation prevents it. Any one who looks at footpaths, 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 havinf5 side slopes, a beaten track on the grass by the stde 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 hack wards 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 m~n, and even of large quadrupeds, have generally twists there, and twists which are \'ery dang::.rous for wheeled carriages in moving rapidly. In the early ages of English history, men and horsemen, a~d pac~-horses, appear to have been the only eng. meers m road making; and as, in a horse with a nder 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 ~re easier for those who walk, or ride slowly, than If the road went straight up. Any one may convince himself of the truth of thes~ effects. of the <:entr~ of gravity by trying to run m a hortzontal duectwn round a hill without getting farther from the summit or centr~ of the hill; ~r how diffi.cult it is to run round on the slope of a Circular basm or hollow without getting nearer to its centre or bottom. If the battlements of a |