Vol. 6, 1920 
GEOPHYSICS: H. S. WASHINGTON 
587 
Among other problems with which volcanology has primarily to deal 
the following may be mentioned: 
Study of the r61e played by earth strains is suggested by Wood, who 
points out that, although such factors as accumulated gas tension and 
possibly others, may enter, yet "a general cause of volcanic extrusion 
[may be] due to the so-called mountain building forces as builders of 
strain, and to certain variable stresses acting as trigger forces." He 
suggests that study of this phase of volcanology would be of interest 
also "to the geological seismologist, the physical geologist, and the stu- 
dent of isostasy." The importance of arriving at some estimate, how- 
ever crude, of the magnitude of volcanic forces, possibly as a measure 
of crustal deformation forces, is pointed out by Wright. 
A systematic and properly conducted study of thermal gradients in 
the crust is suggested by several (Daly, Van Orstrand, and the writer). 
Such a study should be carried out at carefully selected points, the sta- 
tions being chosen with due regard for both the proximity and the ab- 
sence of volcanoes, differences in the underlying rocks and their geo- 
logical structure, the absence of secondary sources of heat (such as the 
proximity of ore bodies), and with proper and well- controlled means of 
measuring the depths and temperatures. It is reasonable to suppose 
that such a systematic project might be carried out with no very great 
difficulty or prohibitive expense. It is needless to say that the results 
obtained by such properly controlled means would be of the greatest 
value for our study of the interior of the earth, and would supersede many 
of the, for the most part, haphazard and not mutually comparable data 
that are now available. 
Connected with this matter is that of the investigation of the thermal 
gradient and the sub-surface conditions in the mass of an active volcano, 
both on its flanks and within the crater. Such investigations might throw 
light on the role of gas inter-reactions as causal in the production or main- 
tenance of volcanic heat, as has been suggested by Day, and they might 
also be of great practical importance in the study of the possible utiliza- 
tion of volcanic heat as a source of energy, a matter to which my atten- 
tion was directed in Italy, both before the war and during the past year. 
The study of the possibilities of regions of geysers and hot springs, as the 
Yellowstone, and in the Hawaiian Islands, along this line, is also sug- 
gested. In this connection the present successful utilization of the soffioni 
at Larderello in Tuscany by Ginori Conti may be recalled. 
The problem of radioactivity as a source of heat, and the possible forma- 
tion of a special committee for this purpose, is suggested by Daly, who 
also suggests the study of the "meaning of the earth's rigidity." 
As minor matters may be mentioned the study of geysers and their 
mode of action, and also the formation or unification of a terminology for 
