GEOPHYSICAL LABORATORY. 143 



This eruption also afforded opportunity to correct a long-standing 

 misconception of the significance of certain cloud phenomena com- 

 monly observed and recorded. The density of the cloud v/hich 

 emerges from the crater is by no means always a measure of the 

 activity within, and indeed sometimes bears no relation to it. The 

 approach of a cold, moisture-laden wind causes an immense apparent 

 increase in the volume of emerging ''smoke," which has no other origin 

 than the condensation of the moisture by volcanic emanations. When 

 the atmosphere chances to be near the saturation-point it will condense 

 in massive white cumuli on coming within range of the volcanic dust, 

 which gives the impression of a great increase of activity without any 

 change whatever in the conditions within the crater. This observa- 

 tion vitiates in large measure the usefulness of any continuous record of 

 volcanic activity which is based upon the apparent volume or height 

 of the cloud from day to day. 



At Vesuvius there is at present continuous activity in two adjacent 

 openings in the crater floor about which a cone of scoriaceous matter 

 and lava-splashes has formed which has now reached a height of about 

 85 meters. The crater floor itself is also rising slowly. In company 

 with Professor Ivlalladra, Director of the Vesuvius Observatory, and 

 guides, Mr. Perret found it practicable to reach the crater floor and to 

 collect both gaseous and liquid ejecta for laboratory study. 



It is a very great misfortune that this period of unusual activity, in 

 which all the active Italian volcanoes appear to be participating, 

 happens to fall in a period of political upheaval, one consequence of 

 which is to impose prohibitive limitations upon the movements of 

 foreigners. It is at the moment practically impossible to continue 

 effective field studies in Italy. 



In Hawaii, both at Kilauea and Mauna Loa, there has been paroxys- 

 mal activity in recent months, and from Mauna Loa a considerable 

 outflow of lava in June of this year. A radial crack opened about 

 half-way up the mountain and from it streams flowed both east and 

 west for a distance of about 8 miles. The flow continued for 6 days 

 only and occurred in a barren and rather inaccessible part of the 

 mountain, so that even the experienced men who chanced to be 

 within reach found difficulty in reaching advantageous points for study 

 and collection during the period of actual flow. Later the sources of 

 the new flow were examined with care, but the gaseous portion of the 

 ejectamenta had then flown and left an irreparable gap in the chemical 

 data available for further study. 



In spite of these various limitations, which are of course inevitable 

 in the study of volcanoes, the elucidation of the volcano problem has 

 made considerable progress during the past year, of which a detailed 

 record v\dll presently be published. 



