HECAPITULATION. 449 



Centre of Gravity, 



1. The centre of gravity is that point in which 

 the weight of a body may be supposed to be col- 

 lected. 



2. A line drawn from that point, perpendicular 

 to the horizon, is called the line of direction. 



3. When the line of direction falls within the 

 base of any body, that body will stand ; but when 

 it falls without the base, the body will fall. 



The Lever. 



1. There are three kinds of levers: 1. When 

 the fulcrum, or prop, is between the power and 

 the weight. 2. When the prop is at one end of 

 the lever, the power at the other, and the weight 

 between them. 3. When the prop is at one end, 

 the weight at the other, and the power between. 



2. In all kinds of levers, the power is to the 

 weight, as the distance of the weight from the ful- 

 crum is to that of the power from the fulcrum. 



3. A bent, or hammer lever, differs only in form 

 from a lever of the first kind. 



4. A balance is also a lever of the first kind, 

 with equal arms. 



5. The statera, or steel-yard, is also the first 

 kind of lever, with a moveable weight. 



Wheel and Axle. 



1. The power must be to the weight, in order 

 to have an equilibrium, as the circumference of the 

 wheel to the circumference of the axle. 



VOL, I, G G 



