H 



B- 



G 



gQ OESEBVATIONS ON- THE 



In order to illuftrate this theory d 



by examples, it will liril be neceiTary 

 to obtain the value of b and w from 

 experiment. Let thenABCDbea 

 wall of any fmall given dimenfions, rKp^ 

 continued from the foundation Z— (^J 

 ABGF, which is of the fame piece 

 of mafonry with the wall, and well fecured in the fo- 

 lid earth ; and to prevent a fraction in any other part 

 than in the line AB, let an inflexible iron bar be ap- 

 plied to the lide BC, fo that a force applied to any 

 point Sy may aft upon the whole fide at once ; and 

 for the purpofe of preferving the center of gravity in 

 a line that bifefts AB in H, (which will fave trouble 

 in the prelent computation) let there be another iron 

 bar of equal weight to the former placed on the op- 

 pofite fide AD. Now let Q, reprefent the weight of 

 the mafs ABCD, including the two bars fufpended at 

 H. Then if W be a weight, acting at S, by a line 

 paffing freely over the pulley />, and fuch as to fuftain 

 the wall and bars in equtlibrio, fuppofing no cohefion 

 in the line AB, we fhall have W : Q, : : AH: AB BS 



and W = j^ — ~\ that is fuppofing AB = 1, BC = 3, 



and BS = 2 = 4H, W will be = I Q. But Q being 

 as ABxBC, is therefore = 3, in this infiance. whence 

 W = ^. Now to determine the force necefiary to 

 overcome the tenacity, let an additional weight w 

 be applied to W, increafing it till it become fufficient 

 for the purpofe, which having a known proportion to 

 the weight W, will alfo have a determinate proportion 

 to Q.. Suppofe, for example, it were found = j W, 

 then, W being =4, *z^ becomes equal \. Now fince 



h = " — - , it becomes equal J in this cafe : which 



two values of/' andw, being thus determined by experi- 

 ment, 



