g4 OBSERVATION'S ON THE 



AB, taking it for granted at the fame time that the 

 foundation HBGF is i'o fixed in the foHd earth, as to 

 require a force to move it, fuperior to that which is 

 required to effect the breakage in the line AB : for 

 ctherwife the whole would turn on the point F, and 

 m.uft be confidered as havino- no adhefion in the line 



o 



FG ; at the fame time the force to feparate it from 

 the earth being eftimated. 



In order therefore to obtain the meafurc of fuch a 

 force as is above Hated, let A' B' and B' C, in the 

 annexed figure, be of any given dimenfions, and let 

 a weight be applied to the point S' in the horizontal 

 diredlion of the center of gravity R, of the triangle 



K C T (which triangle reprefents %• 2. 



the fedlion of the earth refting p c' T' 



freely againft the wall) and deter- 

 mine by experiment, what weight 

 will be necefiarv to break the 



R 



wall, after dedu6ling what would " "/A' E' |B' 

 be fuflicient to fuftain the earth "'f' G' 



in equilibrio, whofe fedtion is reprefented by B' C T' 

 fuppofing there were no cohefion, and call that weight 

 zv — ^let in be compared with the above fuftaining 

 weight. Now fince A is the point on wl^ich the wall 

 is to turn, whatever force be required to feparate one 

 particle of the mafonry in the line A' B', the momen- 

 tum of that particle will be exprelled by multiplying 

 the particle itfelf into its diftance from the point A'. 

 And, from a well known property in the center of 

 gravity, the momentum of all the particles in the line 

 A" B' will be exprelfed by the line itfelf multiplied into 

 the diftance of its center of gravity from the point A' ; 

 which wilithereforebe defined by ^A'B' y A'B'=^A'B'\ 

 Now, fince the weight w is to be applied to the poin*: 

 $3 the momentum of w will be exprciTed by w ^B'S' ; 



and 



