1878.] 
Suspended in Liquids. 
185 
It is very interesting to follow out the effects of this 
pedetic motion from the geological, physiographical, and 
economic points of view. Its importance is immensely 
great, and it is not too much to say that the surface of the 
globe would be very differently shaped were the phenomena 
otherwise than they are. The disintegrating and carrying 
power of pure water mainly depends upon the pedetic 
motion, which, as we have seen, prevents rapid aggregation 
and subsidence. Now, the rain-water which falls upon the 
surface of the earth is sufficiently pure to produce pedesis 
in considerable perfection. Every little stream and pool of 
muddy water bears evidence to this effeCt, and fresh water 
as it flows down the rivers, and even into the sea, continues 
to hold great quantities of silicious particles in suspension. 
But no sooner has the fresh water become mixed with salt 
than the pedesis is destroyed, as I have ascertained by 
direCt trial with sea-water, and the particles subside rapidly. 
Thus we account for the wonderful clearness of ocean- 
water, and the faCt that the ooze from the ocean bottom 
consists almost entirely of organisms produced out of the 
substances contained in solution in the salt water. In the 
same way we may account for the peculiar clearness of 
alkaline solutions, with which I have often been struck. A 
pan of brine at a salt-works, for instance, if allowed to 
stand undisturbed for a little time, becomes as clear as 
crystal. This is due k) the perfect subsidence of all foreign 
particles, in spite of the greater specific gravity of the 
solution which would tend to buoy them up. In the same 
way we may explain the dark blue colour of the Dead Sea, 
which is due to the clearness of the dense solution. 
It now becomes easy to understand the peculiar turbidity 
of glacier streams, for the water proceeding from melting ice 
is in the most perfect condition for producing pedesis. I 
have examined water derived from melting snow, and find 
that the contained air is not sufficient to diminish the sus- 
taining power much, and I have shown that the suspension 
of clay is continued longer in ice-cold water than in warmer 
water. That the particles derived from glacier erosion ex- 
hibit pedesis in a high degree is evident from the silicious 
nature of the rocks eroded, but I have confirmed this infer- 
ence by diredt trial upon the sediment of glacier streams 
both in Switzerland and Norway. As the water from a 
glacier becomes gradually warmed and aerated, the particles 
subside and the water becomes clear ; but there is some 
difficulty in understanding how this process is carried out 
with sufficient rapidity to produce the clear blue water of 
