124 SMALL WATER SUPPLIES. 



from 2 to 2*5. The value of x so found is the mini- 

 mum safe value. The values of Tf and r have to be 

 provisionally settled by the designer, the most suit- 

 able being 



50- H 



while the thickness B of the buttress may be taken as 

 2 in. for every i ft. in value of H. There is an equa- 

 tion for T b but it is of a very complex nature, and its 

 discussion would be out of place in a book of this 

 sort, and certain values are tabulated as under : 



Value of H. Value of TV 



5 5*90 



6 6'8o 



7 7-90 



8 9 'oo 



9 io"oo 

 i o ii '40 



11 12*50 



12 13-55 



13 1470 



14 15-90 



15 17-00 



16 18-25 



17 1875 



18 20 



19 22 



20 23-25 



