288 Archdeacon Pratt on the Thickness of 



This, multiplied by p, is the pressure parallel to the axis of x\ 

 and the projection on the plane yz of an element of the surface 

 = dy dz. The pressure at the point xyz parallel to x will act in 

 the same line as that at the corresponding point when x is taken 

 negative. We may add the two effects together ; this will strike 

 out terms in which odd powers of a? occur, and will simplify the 

 formula. Thus, 



Moment of pressure parallel to x about z 

 = -^dzdyp 4 ^($y+ F*)«(l- •£).» 



after reduction 



= ->/*GeI>Ea 3 . 

 So of the others : — 



Moment about y of pressure parallel to x= j7r^GeDF« 3 5 



33 x 33 





y=-£i7*G6EFfl», 



33 Z 33 





y= ^GeDEfl", 



33 X 33 





33 z= -TTfiGeEW, 



33 V 33 





z=~7rfjLGeT)¥a s . 



These six moments are the same 



as 





Moment about axis of 



x= 



: 0, 



33 33 



y= 



.-^7r/*GeDF0 3 , 



33 33 



z— 



:+^ 6 7r^GeT)E« s . 



These are precisely analogous to the result of paragraph 5. 

 Hence putting 



A G ea3fo r |D^^8/Da % or^for/, 



D being the density of the surface, the effect of the fluid pres- 

 sure on the crust will be to increase f by 



5 Ge __ 5e C a . 5e(l — cos go) a 



128 Dfe~64*singaJ Smflrfld *- 64?asin?a t 



__ 5e sec q& — 1 a , 



64 gatanga J v 



