VOMCANTOC ACTION, HAW ATI. 219 
comes home to us with its full force. On this point we offer a few 
considerations. 
It has been observed that the heat in a pool of lava increases down- 
ward with some relation to the pressure. The cooling influence of the 
atmosphere and surface rocks acts at the surface and would neces- 
sarily make this portion less heated than any part below. Upon this 
principle, were there no other cause to modify the result, the lava pools 
could not be smaller in diameter below than at the surface, and there- 
fore they would continue indefinitely downward ; and any two at some 
distance down—it may be a great distance—would be united so as to 
communicate freely with one another. 
A sketch may help the mind to conceive of the case before us. It 
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MOUNT LOA. 
represents Mount Loa of its actual shape, and shows the diameter of the 
two craters, with the breadth of the conduit below, in case this con- 
duit is as broad throughout as in its upper part. ‘To connect such 
conduits, the union would of necessity be very deep, unless we sup- 
pose what is very improbable, an abrupt convergence below. The 
reader can make the union that seems most probable. ‘The remarka- 
ble breadth of the craters as compared with the elevation of the moun- 
tain will be observed. ‘The longer diameter of Kilauea is four times 
greater than the altitude of the mountain at the place, and that of 
the great lake, which is liquid throughout, is at times fully equal to 
this altitude. 
The lava conduits, if they in fact diminish downward, must owe 
their contraction below to the refrigerating influence of the waters 
that find ingress to the fires. ‘These waters, by which the action is 
kept up, must take a vast amount of heat from the lavas, the absorp- 
tion of nearly 1000° I’. being necessary to vaporization. Moreover, 
the possibility of such a contraction is enhanced by the fact that the 
temperature of fusion of the consolidated rock is higher than that of 
cooling, and the breadth once lost by the conduit, is not therefore as 
easily regained. 
In the walls of the lower pit of Kilauea, which afford sections of the 
material formerly in fusion, I observed one vertical cavity, shaped 
somewhat like an inverted top, though more drawn out below, and 
apparently terminating at bottom in a small conduit. It occurred 
