CENTRE OF GRAVITY. 21 



the body will tumble. Thus the inclining body 

 A B C D (fig. 4.) whose centre of gravity is E, 

 stands firmly on its base C D I K, because the line 

 of direction EF falls within the base. But if a 

 weight, as A B G H, be laid upon the top of the 

 body, the centre of gravity of the whole body and 

 weight together is raised to L : and then, as the 

 line of direction L D falls without the base at D, 

 the centre of gravity is not supported, and the 

 whole body and weight will tumble down together. 



Hence appears the absurdity of people's rising 

 hastily in a coach or boat, when it is likely to 

 overset ; for by that means, they raise the centre of 

 gravity so far as to endanger throwing it quite out 

 of the base, and if they do, they overset the 

 vehicle effectually : whereas, had they kept down 

 to the bottom, they would have brought the line 

 of direction, and consequently the centre of gra- 

 vity, farther within the base, and by that means 

 might have saved themselves. 



The broader the base, and the nearer the line of 

 direction is to the middle or centre of it, the more 

 firmly does the body stand. On the contrary, the 

 narrower the base, and the nearer the line of direc- 

 tion is to the side of it, the more easily may the 

 body be overthrown; a less change of position 

 being sufficient to remove the line of direction out 

 of the base in the latter case than in the former. 

 And hence it is, that a sphere is so easily rolled 

 upon a horizontal plane; and that it is so difficult, 

 if not impossible, to make things which are sharp- 

 pointed, to stand upright on the point. 



From what has been said, it plainly appears, 

 that if the plane on which a heavy body is placed, 

 be inclined, the body will slide down upon the 

 plane, whilst the line of direction falls within the 



