EAR 



q--;-T - - 4- ^ (e* '*) = o an equation which include* nil thr 

 c&ees of rectilinear sloping banks. 



Cor. If the slopes he o, or the dykes vertical, t o t e* ~ o t and c 



5. If the sides be rectilinear, and A D, B C horizontal, to determine 

 the equation of equilibrium of Art. 3. 



The preceding equations have been investigated on the supposition of 

 a perfect connexion of all the parts of the dyke ; they are ,". only ap- 

 plicable to such as are constructed of masonry. 



E 



EARTH, Elements of. 



The principal elements of the earth, according to the determination of 

 La Place, in the last edition of his Systeme du Monde, are as follows : 



Equatorial Diameter ... ........................... 7924 English miles. 



Polar do ........ . ........ ................................ ^908 .................. 



Mean do ........... ...................................... 7916 .................. 



Mean circumference ............................... 218(59 .................. 



Mean length of a degree ......................... 69.08 ............... 



Surface ............................................. 19(5802256 square miles. 



Solidity ........................................ 2597269Ceil6 cubic miles. 



Density of earth about 5 times that of common water. 

 Mass of earth is ------ of the mass of the sun. 



Weight of a body at Equator : do. at the Poles : '. 1 : 1.00569, 

 Length of seconds Pendulum at Equator =. 39,027 in. ; do. at Poles 

 36.197 in. 



Centrifugal force at Equator is about -^- of gravity, and .*. if the ro- 



tatory motion of the earth were 17 times greater than it is, bodies at the 

 Equator would hav no weight. 

 94 



