218 Notices respecting New Books. 



Pasley, at Chatham, on the pressure of earth, with the new and 

 unexpected results to which they led. 



The following extract from some remarks suggested by these 

 experiments, as to the method of resolving the forces adopted bv 

 M. Rondelet, but rejected by M. Mayniel as incorrect and un- 

 scientific, will afford a fair specimen of the ability which has 

 been brought to the support of this important branch of the 

 work. 



" A variety of methods have been proposed relative to the 

 determination of the resultant and direction of the forces of the 

 particles forming the solid DBP2 : some authors having estimated 

 it by the power or force wliich is requisite when acting hori- 

 zontally against the centre of gravity, as M. G., to support the 

 body on the plane; and consequcntiy these have found the point 

 of application to be at 2-Sds of the h.eight of the bank from 

 the bottom of the revetment ; others have found that point to 

 be at one-half of the height, and others again at \-'3d. The 

 latter has been the most general determination, and is obviously 

 the necessary result of a correct theoretical examination and 

 valuation of the direction of the forces : it has been also experi- 

 mentally verified by Gauthey ; but it is necessary to observe that 

 this refers to the interior face of the revetment. Still, however, 

 a singular error was committed in the resolution of the resulting 

 force which was sujjposed to be made at the point F ; so that 

 K F being taken to denote the direction and intensity of the 

 thrust of the bank at F. this was resolved into a horizontal and 

 vertical force at that point which we may denote b) L F and 

 FH ; but the latter of these was rejected, as having no efficacy 

 either in causing the wall to turn aljout the point A, or in re- 

 sisting that motion : — this would have been true, had the wall 

 been merely a line without breadth, because then the points A 

 and B would have coincided, and the force F H would have had 

 its direction passing through the fixed point B : in giving to the 

 line AB, however, any dimension or lengthy it is clear that while 

 the product of L F x L A denotes the efficacy of that force to 

 turn the wall about the fulcrum A ; F H x A B will represent 

 the contrary or opposite moment of the force F H, to resist that 

 motion ; and consequently when these products are equal, the 

 wall will have the same stability as before any earth was thrown 

 at its back ; but when the former product is the greater, the 

 stability will be diminished; and when tlie latter is the greater, 

 the stability will be increased: results which were found to ob- 

 tain from various practical experiment* reported by Col. Pasley 

 in his work above referred to. 



^< We shall come to the same conclusion^ if we resolve our 



forces 



