MECHANICS 73 



in both rows either one or two more than the number of inches 

 of width of the belt, the object being to get an odd total number 

 of holes. For example, a 10-in. belt would have 10+1 = 11 

 holes, and a 13-in. belt would have 13+2 = 15 holes. The 

 outside holes of the first row should not be nearer the side 

 edges of the belt than f in. and not nearer the joint edge than 

 | in. The second row should be at least If in. from the joint 

 edge. In Fig. 2, A is the outside face and B the face next the 

 pulley. The lacing is first drawn up through 1 from the pulley 

 side, and then is carried through 2, 3, 4, 5, 6, 7, 6, 7, 4, 5, 

 2, 3, 8, and out at 9 to be fastened. The other end of the 

 lacing is used on the other half of the belt in the same way. 



HYDRAULICS 



Pressure Due to Head of Water. Hydraulics treats of 

 liquids in motion. When a tank is filled with water, its 

 bottom and its sides are subjected to pressure due to the 

 weight of the water. The distance from a point at any given 

 level in the tank to the surface of the water, measured vertically, 

 is termed the head of water for that level. The pressure 

 exerted by the water is directly proportional to the head. A 

 cubic foot of water weighs approximately 62.5 lb., so that, if 

 a tank 1 sq. ft. in cross-section were filled with water to a 

 depth of 1 ft., it would contain 1 cu. ft., or 62.5 lb., of water. 

 The pressure on the bottom, having an area of 1 sq. ft., would 

 be 62.5 lb., or the weight of 1 cu. ft. of water; consequently, 

 the pressure per square inch would be 62.5 = 144 = .434 lb. In 

 other words, a column of water 1 ft. deep, or having a head of 

 1 ft., exerts a pressure of .434 lb. per sq. in. Knowing this 

 fact, the pressure due to any given head of water may be 

 found by the formula 



p = .434 h, 



in which p = pressure in pounds per square inch ; 

 h = head of water, in feet. 



If it is desired to find the head of water necessary to produce 

 a certain pressure, the formula becomes 



