78 



APPLIED SCIENCE 



of cubic feet passing down the stream per minute multiplied by 

 the weight of a cubic foot of water, multiplied by the perpendicular 

 distance this water falls. This equals the number of foot-pounds 

 per minute. Weight of a cubic foot of water 62.5 Ibs. 



The E. H. P., or estimated horse-power, stored in the moving 

 water is expressed by the following formula: 



E.H.P. 



W XH 

 33000 



Where E. H. P. = estimated horse-power, W = weight of water 

 passing per minute in pounds, H = height it falls in feet. 



78. The Law of Buoyancy. Explanation of why cer- 

 tain substances float on water depends upon what is called 

 the law of buoyancy. When a ship is constructed, it is 

 necessary to lay out the plans in accordance with the prin- 

 ciple or law involved. Consequently a knowledge of the 

 law of buoyancy is important. 



When a body is immersed in a liquid, it is buoyed up by a 

 force equal to the weight of the liquid displaced. The weight of 

 a floating body is equal to the weight of the liquid displaced. 

 The upward pressure, or buoyancy, of the liquid may be re- 

 garded as exerted at 

 the center of gravity 

 of the displaced 

 water, B, which is 

 called the center of 

 pressure or of buoy- 

 ancy. A vertical 

 line drawn through 

 it is called the axis of buoyancy or of flotation (Fig. 50). In a 

 floating body at rest, a line joining; the center of gravity of the 



WATCfi LINE 



FIG. 50. Principle 

 of Buoyancy. 



FIG. 51. Principle 

 of Stability. 



