THEORY OF WALLS. 



97 



in the two foregoing equations. Hence aV »' 

 TiE^^^jilL— « becomes for z=«i/|7/^+^i^— «, 



for ftone walls ; and<2^«^ + 







V^«^4._V^_«for brick walls.— If« be taken = 4 or.2; 

 and the angle TBC 1=45^ fo that s^ beiz.5 ; then^ _, 

 i36x^ for (tone walls, and, 121 1 X^, nearly, for brick 

 walls, both confiderably lefs than Mr. Mullers 

 computations, if w iliould be found what is^here fup- 

 pofed. 



Let A' B' CD' be 



a wall of the fame di- 

 menfions figure 3, with 

 the addition of a coun- 

 terfort B'C'F'E, which 

 is continued to the 

 bottom of the founda- 

 tion G H. Then, fince 

 the breadth of a coun- 

 terfort is i of the dif- 

 tance between each 

 other, the weight ap- 

 plied at any point ^', 

 fufficient to break the 

 counterfort in the line 



-R 



£.».— 



-H*- 



B' E', will be as "TTT^ * which being added to 



the former quantity for breaking the wall A'B'C'D' 



in the line A B, gives w as---j>-H 7^^;-^ — ^• 



Hence the weight fufficient to break a wall of a ly other 



,. p .,, , 2AB*-}-' ECX AB4-i, BC^ «1U , , 



dimennons, will be zz — — X-r and the 



4BC p 



momentum =: ^^ rJ^~ — X t, which if BE be 



4BC ' ' l> 



which mufl therefore be added to the momentum of the 

 Vol. VI. G wall 



n-: BC, will be = 



Trintfdhi Buunex and Gold, Shot-lane. London, 



