44 



Colorado College Studies. 



Forces to he Equated. — The forces to be equated are 

 Impressed force, 

 Pressure, 



Etfective force, and 

 Retarding force, or force lost, 

 which give, when equated, 



impressed force— pressure— effective force= 

 —retarding force, 

 or, in the more usual form, 



impressed force— pressure + retarding force = 

 effective force. 

 It is to be noticed that the sense in which the retarding 

 force is taken is opposite that in which the impressed force 

 is taken. 



Rectangular Co-ordinates. — Take an element PB, the co- 



S H 



B 



FIG. 5. 



ordinates of the point i? being x, y, z and the dimensions of 

 the element being cZo;, dy, dz. 



