54 



MECHANICS. 



tion will fall equally distant within each wheel ; but a 

 shght misplacement, as in Fig. 25, p. 53, will so alter 

 this line as to render it dangerous to drive except on a 

 very even road. 



Thus every one who drives a wagon should under- 

 stand the laws of nature sufficiently to know how to 

 arrange the load he carries. It is true that experience 

 and good judgment alone will be sufficient in many 

 cases ; but no person can fail to judge better, with the 

 reasons clearly, accurately, distinctly before his eyes, 

 than by loose conjecture and random guessing. 



Every farmer who erects a wall or building, every 

 teamster who drives a heavy load, or even he who 

 only carries a heavy weight upon his shoulder, may 

 learn something useful by understanding the laws of 

 gravity. 



It is familiar to every one, that a body resting upon 

 a broad base is more difficult to overset than when the 

 For instance, the square block {Fig. 



is narrow. 



Fig. 26. 



26) is less easily thrown over than 

 the tall and narrow block of equal 

 weight, because, in turning the 

 square block over its lower edge, 

 the centre of gravity must be lift- 

 ed up considerably in the curve 

 shown by the dotted line c ; but 

 with a tall, narrow block, this 

 curve being almost on a level, 

 very little lifting is required. Hence the reason that 

 a liigh load on a wagon is so much more easily over- 

 turned than a low one. 



Of all forms, a pyramid stands the most ffi-irdy on its 



