333+) 
Arr. VILL. Observations on Atmospheric Eletricity made 
on Vesuvius, in June and July, 1819. ' By ¥. Ronarps 
Esq. thee > 
Tue rod of. my electrometer (See Quarterly Journal, Vol. IT., 
page 252,) was ‘placed. perpendicularly on the highest pinnacle 
of the mountain; on the horth side of the great crater, and at 
about 500 yards (across a ravine,) distant from it. It was 
fourteen feet high, and the insulation was very good, for, 
when electrified artificially to a much higher degree than it 
ever became naturally, it retained its electricity for full five 
minutes, without any sensible dimmution. A pair of straws, 
made exactly according to Volta’s standard of the third (or 
smallest) size was attached to the rod. The results were as 
follow, v2z.: 
The electricity was constantly positive. 
The intensity increased as the sun rose (as usual), except 
when influenced by explosions of the volcano, &c: The varia- 
tions of intensity occurred very frequently. The difference be- 
tween the highest and lowest degree of intensity amounted to 
nearly one-third of the mean intensity. 
These variations of tension sometimes accompanied changes 
of wind, which often occurred six or seven times in the course 
of halfan hour. The wind most frequently blew from the south, 
but often suddenly changed to north-east and north. 
Sometimes they immediately followed explosions from the 
craters, and sometimes did not seem to be at all influenced by 
them, or by a wind which came directly from the crater, at the 
time of an explosion. 
Sometimes they were evidently produced by the approach of 
vapour from an aqueous fumerole, and then the tension was 
always increased. Sometimes the tension was diminished very 
rapidly after an explosion, and sometimes increased as rapidly. 
The black fumes from the old crater evidently diminished 
the tension much more frequently than the white, and very 
rarely increased it. . 
Finally, it seemed sometimes utterly impossible to discover 
