Mr Fox on Springs of Water. 67 
Since the water would be at the temperature of the earth at the 
respective depths, and would expand in an increasing ratio as the 
temperature increased, it is manifest that considerable deductions 
should be made from these pressures, but to what extent cannot be 
stated. ‘The forces of water pressure and steam would, on these 
data, probably equal each other at rather more than 9 miles deep, 
and the density of the steam be about four times that of water. It 
is not to be supposed that water can exist, as such, below the zone 
at which it would become converted into steam, if it reach it at all; 
although it is possible that the steam may go much deeper; but as 
its elastic force cannot materially exceed that of the uppermost steam, 
it must be continually lessening in density as it descends into more 
heated parts of the earth. 
Mr Fox referred to the results of observations in mines, which he 
had published from time to time, and which, on being tabulated,* 
seemed to indicate that the heat does not augment in regular progres- 
sion in descending into the earth, but that it increases in a less ratio 
than this. Thus, starting from 50°, the mean of this climate, the 
temperature was : 60° at the mean depth of 59 fathoms, being an in- 
crease of 1° in 35.4 feet; 70° at a further depth of 73 fathoms, 
being an increase of 1° in 43.8 feet; 80° at a still further depth of 
107 fathoms, being an increase of 1° in 60.4 feet.—Temperature 
80° at the depth of 239 fathoms. 
The temperature at given depths has been found to differ much 
in different localities: a fact not to be wondered at, when we take 
into account the greater or less facilities afforded by the cracks in 
the rocks for the circulation of water from greater depths, as well as 
lesser ones. 
If the increase of subterranean heat should continue to be in a 
diminishing ratio much farther down than has yet been penetrated, 
it would seem useless to conjecture at what depth the water and steam 
pressures might balance each other, as that of the former, if present, 
would be always increasing with the depth; and then the question 
remains as to the source from which it can be derived to supply any 
considerable proportion of the existing springs. Mr Fox considers 
that the sea-water can have no tendency, from pressure only, to flow 
into the earth, except at its deepest parts, and these are generally 
very far from land; and that a continued evaporation from it would 
tend to accumulate salt in the deep fissures, so as to interrupt the 
process. However this may be, there is good reason to believe that 
some thermal springs, especially those near voleanoes, may be ejected 
by vapour. He thinks it possible that some of these outbursts of water 
may be caused by the pressure of the ocean, which, from its greater 
* See Mr Fox’s Report on some observations on subterranean temperature— 
Report of the British Association for 1840, p. 309. 
