STORAGE AND DISTRIBUTION. 



157 



in other words, if r equals the internal radius and 

 R the external, the back of the pipe is strained less 

 than the face in the ratio r L : R 2 , and the mean strain 

 is equal to 



2r*s 

 W^ (47) 



upon which is based all empirical formula for thick- 

 ness. 



./.^..jWjW.) . . (4 8) 

 Vio *) \25,ooo/ 



/ being the thickness, d the diameter in inches, and 

 H the head in feet. 



