THEOP.Y OF WALL3. QB 



and this quantity, from the nature of the problem, 

 mufl be as -^-A'B' : confequentlyj we have zv as 



5^ . Now, this beino; determined, the weidit w 



BS ' ^ ^ JD 



may alfo be determined which will break any other 

 wall, \mder the like circumftances, whatever may be 

 the dimenlions of AB and BC (or BS) as in figure ill* 

 For feeing that it will be in the conftant ratio of -^AB'' 



diretftly, and BS inverfely, and if — be called k, 



BS 



we (liall have W : -ze; : : ^i-L : ^, andW ; — ^ — .-', and 



B s B s X i? 



therefore WxBS= i^'iil'',themom£ntumofW;— 



which quantity muft be added to the momentum of' 

 the wall given by Mr. Muller. 



Now, if AE^mi, EB = .r, BC= a, and there- 

 fore BS = 4- ^, according to Mr. Muller's firfi pro- 

 file ; then iA^ J^>-'^^' ; which added to 

 his equa tions for flone walls, we have x- 'f'lfiax + ^rrn^ 

 + "^ 7 — - — = /-^ s^ a^ and therefore 2// -;- c:? X .t* 



'\-'lh'Vzvy.2nax^=a'^ x'^ s^ h — i/' + '-ff x?/-* Vv'hich, re- 



duced, gives .r=^v'«^ + -——2^^.^ ^^, a 



general theorem for ftone walls^ whatever be the value 



of ^ and 1&J. 



Since the fpecific gravity of ftone to that of brick 

 is as 5 to 4, if the above momentum for the wall be 

 reduced in that ratio, or its equal (,l s^ a ^) jncreafed ; 



there will arife x^ -I- 2?/^;? t- ' n"- a- ^- 4_^fili'^= ' ^ s^ a\ 



which reduced gives x = ^^/^?^-^' -j ^^ ^ /' ^ ^ ^'^ 



— ^^> a general theorem for brick walls. 



In 



