Vol., 6, 1920 
GEOPHYSICS: H. S. WASHINGTON 
589 
important item in the routine observations at a volcano station ; the former 
entering into the question of the "trigger forces" needed to start an erup- 
tion, and the latter as bearing on the question of the origin of the water 
present in volcano clouds and gases. 
Humphreys called attention some years ago to the influence of the 
finest volcanic dust, blown into the upper regions of the atmosphere dur- 
ing first magnitude eruptions and suspended there for prolonged periods, 
in lowering the solar constant of radiation, and thus affecting the weather 
over wide areas for long periods. This has been invoked to account for 
periods of glaciation. A knowledge of the chronology of volcanic eruptions 
is necessary for their proper correlation with meteorological and radiation 
data, and the further study of this theory. 
In this connection mention may be made of the possible utility of the 
study and identification of volcanic dust collected at great distances from 
a volcano in eruption, as bearing on the study of the currents of the upper 
atmosphere. 
The possible influence of the supposed blanketing effect of carbon dioxide 
on past climates has long been a favorite hypothesis, and as it is known 
that this gas is given off by volcanoes, a possible line of research is indi- 
cated connecting climates with periods of great volcanic activity — a 
matter that has already received some attention. 
A minor problem, and one that has been little studied, because of the 
rarity of its occurrence, is that of the blue or green color presented by 
the sun during some eruptions, as that of Krakatoa in 1883. Especial 
attention might be paid to this by the observers of future eruptions. 
VOLCANOLOGY AND TERRESTRIAL MAGNETISM 
Bauer calls attention to the "local changes in the distribution of the 
earth's magnetic forces in the neighborhood of volcanic eruptions." He 
also lays special stress on the investigation of such phenomena as the 
world-wide magnetic disturbance that took place coincident with the 
eruption of Pelee in May, 1902, and the fact that no such world-wide 
disturbances seem to have occurred in connection with that of Krakatoa 
in 1883. This is a problem in which the observations of local observers 
might be of great value, were their attention called to its importance 
and their observations properly directed. The lightning flashes in the 
volcanic cloud, and other such phenomena, during eruptions, are also of 
interest and are probably worthy of study. 
Bauer also suggests the problem of electric currents in the earth's 
crust during volcanic eruptions, such as have been observed by Palmieri 
at Vesuvius. A minor point is the magnetization of lava flows, and that 
of clay beds covered by them; while there might also be mentioned here 
the study of fulgurites — the vitreous tubes and patches formed by light- 
ning strokes fusing the rock of the summits of volcanoes, (as Ararat), and 
other places. 
