ON PRESSURE AND EQUILIBRIUM. 63 



The stability of a body supported on a flat basis, of a given extent, is of a 

 different kind, and is independent of equilibrium. For here, if the centre of 

 gravity niove either way, it -must begin its motion in an inclined direction, 

 instead of describing- a curve which is initially horizontal. The stability of 

 such a body becomes less and less, as it is more and more inclined, till, when 

 the centre of gravity is vertically over the margin of the basis, there is a tot- 

 tering equilibrium ; and if the inclination be still further continued, the body 

 will tall. (Plate III. Fig. 43.) 



The broader the basis, and the lower the centre of gravity, the steeper must 

 the path of that centre be, and consequently the greater the stability. Thus 

 the disposition of the weight in a carriage may considerably aft'ect its stability, 

 by altering the place of the centre of gravity. A waggon loaded with iron is 

 much less easily overturned, than when it is loaded with an equal M-eight of 

 hay; supposing the inequality of the road, of any accidental obstacle, to ele- 

 vate one side of the waggon, it will always recover its position, provided that 

 the centre of gravity remain within the vertical line, passing tlirough the point 

 of contact of the lower wheel and the ground ; and it is obvious that the 

 higher the centre of gravity is situated, the sooner it passes this line. If 

 the velocity of the motion' were very great, the wheel which is elevated 

 might be lifted off the ground by the momentum, and the centre of gravity 

 might thus be carried beyond the vertical line, by means of an obstacle which 

 would not have overset the waggon, if it had been moving slowly. (Plate III. 

 Fig. 44.) 



If a person be sitting or standing in a carriage, the part of the carriage on 

 which he sits or stands may be considered as representing the place of his 

 weight, provided that his situation be always perpendicular; but if the motion 

 be rapid, he will not be able to remain constantly in a posture perfectly erect, 

 and the centre of gravity of the carriage, with its pas.sengers, Avill be some- 

 what more elevated, than it would be on this supposition. 



The direction of the initial motion of the centre of gravity readily explains 

 the suspension of a weight, or a bucket of water, on a rod resting, on the end of 

 a table, when another rod is employed, to keep the bucket at such a distance 

 from the end of the first, that the centre of gravity may be under the table ; 



