OF PRESSURE AND EQUILIBRIUM. 85 



-^^)x220and^!^(^-\-j^)x94, of which the diffe- 



rence is , or .0yo4o od, and its square root about 



a 



8070 feet. Hence, if the velocity of a projectile from the 



moon exceed 8070 feet, it may pass the neutral point, and 



descend to the earth, where its velocity will become more 



than 36000 feet in a second. 



SECTION III. OF PRESSURE AND EQUILIBRIUM. 



238. "281.'' Definition. A pressure 



is a force counteracted by another force, so 



that no motion is produced. 



Scholium. Thus we continually exert a pressure by 

 means of our weight, upon the ground on which we 

 stand, the seat on which we sit, and the bed on which we 

 sleep ; but at the instant when we are falling or leaping, 

 we neither exert nor experience a pressure on any part. 



239. " 282.'' Definition. Equal and 

 proportionate pressures are such, as are pro- 

 duced by forces, which would generate equal 

 and proportionate motions in equal times. 



240. " 283." Theorem. Two contrary- 

 pressures will balance each other, when the 

 motions, which the forces would separately 

 produce in contrary directions, are equal; 

 and one pressure will counterbalance two 

 others, when it would produce a motion equal 



