Experimental Philosophy. [Lecture 15. 



direction falls within such base ; for in this 

 /the body cannot be made to fall, without 

 first raising the centre of gravity higher than it 

 was before. Thus, the inclining body ABCD, 

 (fig 92.) whose centre of gravity is E, stands 

 firmly on its base CDIK, because the line of 

 direction EF falls within the base. But if a 

 weight, as ABGH, is laid upon the top of the 

 body, the centre of gravity of the whole body 

 and weight together is raised up to L; and 

 then, as the line of direction ID falls without the 

 base at D, the centre of gravity I is not sup- 

 ported ; and the whole body and weight tumble 

 down together. 



As a practical illustration of this, I shall 

 mention that the tower of Pisa (fig. 93.) leans 

 sixteen feet out of the perpendicular, and stran- 

 gers are consequently afraid to pass under it. If, 

 however, the materials will hold together, there 

 is no necessity for any such apprehension. For 

 if the plummet c is let fall from its centre of gra- 

 vity, you will see that the line of direction is 

 within its base or foundation, and therefore it 

 has stood without a miracle these three hundred 

 years. 



The nearer the centre of gravity and the line 

 of direction coincide, the firmer any body stands 

 upon a horizontal plane. If the plane is inclined 

 a body will slide down it, if the line of direction 

 falls within the base; but it will tumble down 



