J. D. Dana — History of the Changes in Kilauea. 227 



of liquid lava no vesiculation could have taken place at this 

 depth inside of the conduit ; but at the discharge, the lavas 

 escaped from the pressure, and the vesiculation by means of 

 the "diffused moisture must have then begun. Whether the 

 vesiculation for the whole stream took place at or near the 

 source cannot be decided without more knowledge of the flow 

 and its actual sources than we now have. (See further on the 

 Summit crater, in a future part of this paper.) 



(4) The facts also tend to sustain the conclusion, before 

 expressed, that the ingress of the subterranean waters, what- 

 ever their source, took place by molecular absorption ; for it 

 produced an essentially equable molecular distribution. 



d. The distribution and functions of moisture after recep- 

 tion into the conduit. — (1. ) The above conclusions from the vesi- 

 culation have prepared the way for additional deductions as to 

 the distribution and movements of the moisture in the con- 

 duit. After its reception, it is exposed to a heat at least 1500° 

 F. beyond the critical point of water (773° R) and retains the 

 temperature of fusion to the surface. If the expansive force 

 has at the ingress under the pressure any effective value, the 

 accession of the moisture will diminish somewhat the density 

 of the lava, that is, increase its bulk ; and this increase will be 

 greatest along the central region of the conduit because this is 

 the region of greatest heat. If dissociation takes place, the 

 increase is still greater, as it adds to the bulk of the moisture. 

 It is a question, therefore, whether the pressure of the denser 

 lateral lavas of the conduit would not have some effect toward 

 producing an upward .movement along the hotter central 

 region. 



(2) The mechanism of the volcano, as regards these inside 

 vapors, seems then to be this : (1) a molecular absorption, at 

 depths below, of subterranean waters from regions either side ; 

 (2) a rise of the lavas, thus supplied with moisture, along the 

 conduit from some cause (see beyond on "the ascensive force 

 of the conduit lavas ") and perhaps partly in consequence of 

 the vapors present ; (3) after reaching a level where the pres- 

 sure is sufficiently diminished, a union of the molecules of 

 water into gas- particles, producing by their expansive force 

 vesiculation' (4) a further union of particles into bubbles, 

 when the vapors are sufficiently abundant, in order to exert the 

 greater expansive force required to escape through the surface 

 of the lavas, producing projectile results. 



e. Mechanical effects of vesiculation. — Yesiculation tends in 

 a quiet way to increase bulk, as the above mentioned facts illus- 

 trate. It therefore will give increased height to the liquid 

 lava in a conduit. How deep down this effect is appreciable is 

 a point of much importance in its bearing on the movements 



