TOWERS AND TANKS FOR WATER-WORKS. 



total pressure acts against it in many directions, which might 

 be represented by an infinite number of radii drawn from o as 

 a centre. But let it be required to find the horizontal pres- 

 sure in Ibs. in one direction only, say parallel to o e, or perpen- 

 dicular to a d, which would be the force tending to tear the 

 curved surface away from the flat sides a b n v, and d c s k, 

 by producing fractures along the lines a v and d k, or which 

 would tend to burst a pipe or other cylinder. In this case* 

 multiply together the area of the vertical projection a d k v in 

 sq. feet ; the depth of the centre of gravity of the curved sur- 

 face in ft. (which in the semi-cylinder would be half of e m, 

 or of o i), and 62.5. 



" Since the resulting pressure is resisted by the strength of 

 the vessel along the two lines a v and d k, it is plain that 

 each single thickness along those lines need only be sufficient 

 to resist safely one-half of it ; and so in the case of pipes or 

 other cylinders, such as hooped cisterns or tanks." 



FIG. 10. 



Resistance offered by Material. From the above, it will 

 be seen that a formula for hydrostatic pressure exerted 

 upon the sides of a cylinder would be 



DX HX 62.5 





where D = diameter of cylinder ; 

 H = its height in feet. 



