relation to the Constitution of the Earth's Crust. 15 



whence, remembering that -¥- = -=- e, 



h 2 

 ju t) + z*-=hu — 



which shows that 



( -q-c — /i t) + z 2, = hu— -x — (<T—lJL)(tW — kt— ■% V 



ft 2 o— m/ , * 2 



11 7 o-— /^ 

 -s- C — ll -t 



3 p 



When the masses are regarded as cylindrical, u = iv, and 

 gph =g / (^cr—fjb)t ; g' being less than g by a quantity of the order 



of — , which, on account of c in the denominator of the frac- 



c 7 7 



tion, may be neglected ; and, finally, 



<T — 



P 

 Z< 



'(«♦!)-! 



11 <7 — [A , 



3 p 



If we give to h the extreme value of 5 miles, and make &=25 

 miles, £ = 50 miles, and putting /Lt=p = 2*68, and cr=2*96, 

 c = 3953 miles, we get 



Eise of sea-level less than 90 feet. 



But if we take the height of the plateau at three miles, the 

 rise of the sea-level will be only 17 feet. These are very much 

 less than former estimates *. If what precedes is correct, we 

 are justified in accepting the observed heights of the stations 

 as their true heights f . 



It will be noticed that the condition of equilibrium has 

 caused u, the radius of the plateau, to disappear from the 

 expression for the rise of the sea-level. It does not, however, 

 follow that the same rise would be occasioned by a conical or 

 dome-shaped mountain as by an elevated plateau, because the 

 result has been obtained on the supposition that the radius is 



* I am unable to follow Archdeacon Pratt, where he seems to state 

 that an attenuation will raise the sea-level at a station above it, and makes 

 the rise at More nearly 1000 feet (p. 214, 4th ed.). 



t It follows from the above that, in the case of extensive floating fields 

 of ice, their effect to raise the sea-level around them w ould be incon- 

 siderable. An ice-cap resting upon the sea-bottom might be regarded as 

 a mountain of ice, and its effect estimated accordingly. 



