1 8 The American Geologist. January, 1905 
in geodesy and terrestrial magnetism, and cast backward 
through the vista of time a ray of Hght on the nebular hypo- 
thesis. 
Again, when the law of elasticity and the approximate 
constitution of the globe are known, it will be possible to 
work out a satisfactory theory of the simpler modes of vibra- 
tion in a terrestrial sphere, and then seismological observa- 
tions can be applied to determining more precisely the in- 
trinsic elastic moduluses of the earth along the paths of 
earthquake waves. 
It will also be practicable to examine critically the pos- 
sible rupture of the globe as a consequence of change of 
figure and to study intelligently the simpler cases of the 
crumpling of strata, fissuring and other problems in the me- 
chanics of orogeny. 
The science of elasticity has had a very disappointing 
history. Simple as is the assumption ?// tensio, sic vis, the 
attempt to solve even such seemingly elementary problems 
as the flexure of a uniformly loaded rectangular bar leads to 
insoluble equations ; so that the science has been relatively 
unfruitful. It remains to be seen whether a truer relation 
between load and strain will not simplify formulas and in- 
crease the applicability of algebra to concrete cases. 
From an astrophysical point of view the dialytic action 
of mineral septa is unimportant, but it has a very interesting 
bearing on metamorphism and ore deposition, and may read- 
ily contribute to economic technology. 
The relations of viscosity to the diffusion of matter have 
not yet been elucidated even for ordinary temperatures. This 
subject is one of much importance in connection with the 
genesis of rock species, and of course it should be studied at 
10 degrees before undertaking researches at 1,000 degrees. 
High temperature work is essential even in the investi- 
gation of the elastic problem and it is almost a virgin field. 
Even thermometry is very imperfect above the melting point 
of gold, though it is destined soon to become exact at least 
as high as 2,000 degrees, a range which will probably suffice 
for geophysics. But we are also in almost total ignorance 
of the extent to which the laws of physics, studied at ordinary 
temperatures, prevail at one or two thousand degrees. One 
