20 Rev. O. Fisher, An attempt to explain [Oct. 25, 
There is no @ priort reason why the applicability of the 
physical law should be confined to the ordinary range of tem- 
perature, or why the relations between a substance, as rock, which 
is not liquid at a lower temperature than (say) 3000° Fah., and a’ 
substance, as water, which is not a gas under about 700° Fah., 
should differ essentially from those between a substance (water) 
and a gas (e.g. carbonic acid), which are respectively liquid and — 
gaseous at ordinary temperatures. It is quite possible that the 
solubility of water-gas in molten rock may be as great as that of 
carbonic acid in water, in which case we should have m about 
equal to unity. But apart from experiment, there can be no 
certainty upon this ratio. 
If the fused rock is saturated with gas at all depths, the mass 
of the gas dissolved by a given quantity of it will be greater at 
greater depths on account of the increased pressure there: and 
if, on the pressure being relieved from that required for saturation, 
vesicles of gas are separated from it, these must be subject to 
the liquid pressure of the magma. 
Let the magma be exactly saturated at every depth ¢ under 
the pressure ow at that depth. It will consist of fused rocky 
matter and dissolved gas, without any vesicles of free gas, and if 
the density of the rocky matter is o, the density of the magma 
will be o+ya. We may regard the force of gravity (g) as 
constant for the depths we intend to deal with, and we have to 
determine a, 
o=g|(o+ ye) dé. 
Suppose there to be a solid cooled crust of thickness k and 
density co. Then 
= e +gok) Ue ee 
a, 9Y 
In fact the crust must be of less density than the substratum, 
being probably about 2°68 (that of granite); while o=2-96 (the 
density of basalt). The false assumption can be corrected by 
giving a compensatory less value to k. 
We can now see what is the order of magnitude of the pro- 
duct ygé. For since the density where the pressure is @ will be 
o +a, if we put for o the value just obtained, we find under the 
pressure of a column of the saturated magma, including the 
pressure of the crust, at the depth ¢, 
79 = log. = — log. (1 + ygh) 
l Oo 
< OS ee 
