418 F. A. Ferret — Vesuvius. 



appear in the photograph as a mere speck, quite useless for 

 the purpose of measurement. 



2. The lavas of most interest at present are the sub-terminal 

 flows of 1905-6 on the west-southwest flank. The accumula- 

 tions of 1881-3 and 1885-6 have too far cooled down to be 

 interesting, and the same may be said of those of 1891-4 and 

 1895-9 (Colle Margherita and Colle Umberto), although these 

 still exhibit sensible surface temperatures with slight fumarolic 

 action.* The most recent lavas — those of the rapid lateral 

 outflows on the southeast flank during the last eruption — have 

 cooled rapidly and show high temperatures only at or near 

 their mouths of emission, where fumaroles bring hot vapors 

 from the interior. In comparison with these the sub-terminal 

 flows of 1905-6 on the west-northwest flank of the cone have 

 shown a comparatively slow cooling. At a certain point 

 where the path of ascent crosses one of the streams, Mercalli, 

 in April, 1907 found that lead wires were fused while those 

 of zinc were not, indicating a temperature between 325° and 

 412° C. In February, 1908 wires of tin were melted but 

 not those of lead, indicating between 228° and 325°. On 

 March 5, 1908 my electric pyrometer showed at the same 

 point 244° and on September 3, 1908 it indicated 140°. On 

 July 10, 1909 this had fallen to 65° C. On the main stream, 

 which is somewhat farther to the south, the lava has greater 

 depth and showed in July, 1909 a temperature of 175° C. 

 This is at a point some hundred meters farther down the cone 

 and is the site of the secondary fumaroles which have shown 

 sublimations, as recorded in section 3. 



There is also a sheet of lava on the north-northeast side of 

 the cone under the " echancrure." The exact date of its 

 emission is somewhat of a mystery, although it was probably 

 during the early part of the last eruption. As a lava-stream 

 it is of little importance, being of small volume and forming 

 a self-arrested cascade of glacier-like appearance, but its out- 

 flow on this side of the cone was, in my opinion, one of the 

 causes of the formation of the " echancrure." Photographs, 

 far too numerous for reproduction, have been made of this 

 and other characteristic details of the volcano in the belief that 

 they will be useful for comparison in the future and in order 

 that all features of the present repose-period may be properly 

 recorded. 



3. The fumaroles offer the most important field for investi- 

 gation during the periods of repose, and it is regrettable 

 that these have not been systematically observed. It is true 

 that deposits and sublimates were collected after the erup- 



* Mercalli observed the lava of the Colle Umberto still incandescent in 

 1901, and I was able to char a stick in the crevices as late as 1905. 



