22 Rev. O. Fisher, An attempt to explain [Oct. 25, 
the surface pressures. Suppose the surface pressure corresponding 
to p.to be goc, we then get the value of p from that of a by 
subtracting gok and adding goc in its place, 2.e. by subtracting 
go (k—c); whence 
mga (k —c) 
ca 0 (£+gok) evs — 2 —go (k- ; BS 
af ay 
Observing that z and ¢ begin together, we obtain by inte- 
gration 
m (k — ¢) | l+yg(k-—c)(1- = 
z= €+ ———___—... log, 1 + ——4++___-—_“} 
e+ Tt og 0) 796 
To obtain an approximate expression for the upswelling of the 
column, suppose that the depth of the substratum is 7 times that 
of the crust, or €= nk, k being taken at 25 miles*. 
Then yo (€+k) = : =), suppose, 
1 
and 195 ae 2 ea Xr 
Substituting these rth we have by expanding and neglect- 
; : mr \* 
ing terms in = ; 
z2—C km (n )e- mr 
Foam meg Ltn - G 1 at el 
-_ 
mr \? 
+ terms in al \ {l—yg (k—c)}. 
The interpretation of this equation will depend upon the value 
of the ratio 2 Since ¢ is less than & this will be greater than 
unity. But if it be less by only a few feet, & being taken at say 
about 25 miles, — may be put equal to unity, and then, 
Bit on c yates? 
eee mM flog. (1 +n) 5 ( ) Xr 
l+n 
k—c. mr 
es! crt {1 —yg (& — ©)}. 
We have seen that if €+, which is the depth from the surface 
down to the supposed solid core, is 250 miles yg (€+ %) or » 
* See the author’s Physics of the Earth’s Crust. 
