F. A. Perret — Volcanic Vortex Rings. 



107 



iigs. 1 and 2 were projected from crater JSfo. 7. These had the 

 same color as the other vapors and the air was full of a fine 

 red ash having a strongly acid reaction. The large amount of 

 this ash present in the air may be inferred from the aspect of 

 the sun in the lower portion of fig. 2, which appeared as a 

 ball of burnished copper, and was photographed without irradi- 

 ation effects. 



This production of ash continued along the first few hundred 

 meters of the lava stream where the gases still escaped from the 

 surface in considerable quantities. The gas emission under these 



Fig. 2. 



conditions is apparently very gentle (fig. 6), producing a con- 

 tinuous simmering sound analogous to that of water in a kettle 

 just before ebullition, but it is probable that each tiny gas 

 vesicle burst from the lava with an explosion wJiich, for its 

 size, is violent, and thus projects and carries off minute parti- 

 cles of the exploded shell. 



It is this subdivisional gaseous expansion, and not the 

 explosion of large bubbles, which is the cause of the formation 

 of the ash. 



The degree of viscosity of the lava is, in all probability, an 

 important factor in this direct formation of ash, while secondary 

 to the gas content as a determining cause. In the case we are 

 considering, although the velocity of the stream at this locality 



