SHALER: EXPULSION OF GASES. 
93 
lessens, and it is thus easier for the other vesicles to find their way 
upward by the path; in a moment they pursue each other in a pro¬ 
cession ; the more there are of them the easier the ascent and the 
more rapid the movement. In certain cases we can note the bubbles 
coalesce so that a blowing point is formed on the surface of the 
liquid. We thus see why the least passage of the gas from its dis¬ 
solved state to that of a vesicle may determine in a fluid the forma¬ 
tion of an upward setting column of discharge. If we allow the 
champagne to remain unshaken until it has ceased to produce gas 
bubbles, we may note another fact which has an even more impor¬ 
tant bearing on the problem, for at a slight blow, the small equiva¬ 
lent of an earthquake shock, the fluid will instantly disengage a 
large amount of gas which passes at once from the invisible dissolved 
to the aggregate form of the bubble, and at once the upward 
channeling of the liquid by the procession of vesicles is renewed. 
With care the process of rest and activity can be repeated at least 
half a dozen times before the supply of gas is exhausted. 
The facts which we obtain from the observations made in the 
development of ascending channels in a fluid may not at first sight 
appear to be applicable to the problem we have in hand, for the reason 
that the earth is apparently not comparable to a liquid, the water in its 
interstices not exceeding at most one sixth and generally being less 
than one tenth of the mass. To remove this apparent difficulty in 
the application of the experiment to the case in hand, we may note 
certain other tests and experiments which bear upon the subject. 
By adding sugar to the effervescing fluid we can see that as the" 
mass becomes more viscous the ascending columns are further apart 
and that the freeing ground of each is thus made wider. This is 
due to the fact that the strain required to effect the displacement 
of the liquid is increased. The same effect is evident in the boiling 
of any such substance as tar; the gases or vapors which are formed 
next the heated bottom have such difficulty in breaking their way 
in the vertical channel that they may unite in the lower part of the 
vessel pushing the whole of the material before them, in which case 
the pot boils over. We thus see that the formation of the ascend¬ 
ing passages, chimneys, as we shall hereafter call them, depends upon 
an equation between the ascensional energy of the gas and the resist¬ 
ance which the material opposes to movements of the gases to the 
paths of escape. A similar observation may be made with yet less 
fluid materials, such as leavened dough ; in this material we may note 
