112 J. D. Dana— Volcanic Action. 
abundance that they could not be driven back by the steam 
made at their approach to the fires; and they consequently 
entered,—the opened mountain having made upward escape 
for lavas and steam possible; and thence came the steam power 
for the grand occasion. And perhaps, the cooling action of so 
large a body of water may have put the surface-fires out, leav- 
ing the heat, however, in possession as before, at no great depth 
below. 
Cinders are projected to a greater height at Vesuvius, and in 
most other volcanic regions, than at Kilauea; but this is proof 
simply of greater viscidity in the lavas; and the projected lavas 
fall in cooled masses or cinders because of the height of projec- 
tion. Greater viscidity leads to the production of larger vapor- 
made bubbles before the explosion, and therefore fewer of them 
over a given surface of liquid lava; and, in times of moderate 
activity, the number may be only half a dozen or a single one 
at a time, while, on a like area, lavas with the Kilauea degree 
of viscidity would have scores. When at Naples, in May of 
1834, there was at night an interval of seven to eight minutes 
between the explosions or the throw (some hundreds of feet in 
height) of fiery cinders; on the ascent, the following day, of 
four to five minutes; and on passing Stromboli, a fortnight 
later, June 16th, of fifteen to twenty minutes—the activity be- 
ing less than usual, explosions every 2 or 8 minutes being com- 
mon. As Spallanzani, Hofmann, and others have seen the 
rising bubble within Stromboli, the bursting, and, following 
this, the rush of vapor and the cinder projections, there is no 
reason to doubt that at Vesuvius, also, each throw of cinders 
has the same source. Mr. John Milne states that on his ascent 
of the Japan volcano, Oshima, in May, 1877, on approaching 
the top, successive explosions were heard every two seconds 
with occasional pauses, which explosions he found, on reaching 
the top, to be due to successive outbursts of steam, each pro- 
jecting ashes and bombs to a height of nearly 6000 feet, that 
fell vertically unless wafted by the winds.* 
At the eruption last June in New Zealand, above referred 
to, the “tremendous roar” of the craters that added to the 
terrors at Wairoa, five miles distant, was at Auckland, 120 
miles away to the northwest, resolved into ‘‘a series of detona- 
tions, like the firing of a prolonged salute af minute imtervals, 
with an occasional lull.”+ This fact signifies that only the 
heavier of the aerial vibrations reached that place. - The roar 
heard at Wairoa was due to the simultaneous explosions in the 
several active craters and the storm and earthquakes; and 
* Volcanoes of Japan, Trans. Seism. Soc. Japan, ix, part 2, 1886. 
+ Volcanic Eruption at Tarawera with an account of the Thermal Springs dis- 
trict of N. Zealand, by T. W. Leys. 
