70 Mr Fox on Springs of Water. 
the densest clay, against the force of mechanical pressure; and he 
has succeeded in shewing, that subterranean currents of electricity 
are capable of producing this effect. The veins of clay in the earth 
may, therefore, act an important part in filtering the water chemi- 
cally, as well as mechanically, as they undoubtedly do, in supporting 
springs at different levels, and in greatly limiting the influx of water 
into the mines, which, without them, could not be worked much 
under the surface; so that, although they lie hid in the earth, and 
comparatively little known, they may be numbered among the adap- 
tations designed to meet the wants of man, by an all-wise and bene- 
ficent Creator. 
Since Mr Fox’s paper was read, he has partly filled one branch 
of a U-shaped glass tube with sea-water, and the other branch with 
spring-water, the two fluids meeting at the bent part of the tube. 
Under these circumstances, they exhibited no tendency to become 
mixed ; for, after many days, the original difference in the heights of 
the two columns had not perceptibly altered. The case was the same 
when water and strong brine were balanced, in like manner, against 
each other, although the apparatus was heated as much as 200° for 
some time. Neither did a mixture readily take place between fresh- 
water and sea-water, in an upr ight glass vessel. In this instance, the 
fresh-water was slightly coloured, and carefully poured on the sea- 
water, when the line of division appeared to be well defined, and be- 
came still more so after the vessel, with its contents, had afoul some 
time in water, at rather above 200° Fahr. The heat produced in each 
fluid upward and downward currents, which were quite independent of 
those in the other, so that their surfaces of contact were undisturbed.* 
Hence it appears, that the freshness of springs, at the surface of 
the earth, affords no evidence of the non-existence of salt water 
under them, at considerable depths: while the presence of common 
salt in some springs, the greater specific gravity of sea-water, and 
the unbalanced pressure in the deepest parts of the ocean, rather 
favour such an assumption. 
Mr Fox suggests, that the surfaces of deep rivers will, from the 
inferior specific gravity of their waters, have a tendency to be at a 
higher level than the sea at their conjunction ; and that, as the fresh- 
water flows down to equalize their levels, the sea-water will have a 
disposition to pass under the former, to equalize their pressures. 
* Tt was found, after two days, that the upper part of the sea-water 
had become a little coloured, indicating some tendency, small as it was, 
in the fluids to combine, owing, doubtless, te an endosmose action ; for 
when heated, ‘wo lines of division appeared, at equal distances from 
where the first line was,—above and below it,—and the included fluid 
was less highly coloured than the water, the sea-water remaining with- 
out colour. 
