Present Problems of Geophysics. — Becker. 19 
of the less difficult problems of this group is that of thermal 
conductivity and specific heat of solid bodies at high tem- 
peratures. For the principal metals this is already known as 
far as 100 degrees, but not for rocks or minerals. It would 
be especially desirable to have such determinations for gran- 
ite, basalt and andesyte, the last representing the average 
composition of tlie accessible part of the lithosphere. 
It seems to me that when the thermal dififusivities are 
known for these rocks, over a range of a thousand degrees, 
the question of upheaval and subsidence can be attacked with 
a good prospect of success. A cooling sphere is conceiv- 
able in which the distribution of thermal diffusivity is such 
that the flow of heat would be "steady," in Fourier's sense, 
and thus accompanied by no superficial deformation. With 
any other distribution of dififusivities, deforniation would oc- 
cur, and the globe would act as an imperfect heat engine, 
the work done being that of upheaval or subsidence. Now 
when the assuredly variable value of difTusivity for the mate- 
rials of the globe is known, the mathematical conditions for 
steady flow can be worked out, and if these are not consis- 
tent with the facts of the globe, a vera causa for upheaval will 
have been found, which may lead to further and more detail- 
ed conclusions. It should also either elucidate or simplify 
the subject of fusion of magmas and their eruptive expul- 
sion. 
The data for constitution and thermal dififusivity will 
readily be applicable to the problem of the earth's age and 
will yield a corrected value of the probable lapse of time since 
the initiation of the consistentior status of the Protogaea. 
The most difficult field in geophysics is the study of solu- 
tions at high temperatures. This is largely because both 
methods and apparatus require to be mvented. When w'ork 
of this kind was undertaken in the laboratory of the Geolo- 
gical Survey, three years since, no furnace existed in which 
pure anorthite could be melted and a trustworthy determin- 
ation of the temperature of fusion made. For the study of 
aqueo-igneous fusion which must, of course, be formed at 
considerable pressures, extremely elaborate preparation is 
necessary ; indeed, all attempts hitherto made in this direc- 
tion have been only very partially successful. 
