UNDER THE APPLE-TREES 
shore in Alaskan waters, or when the campers in the 
forest heard a tree fall in the stillness of the night. 
In both cases the tree’s hour had come; the balance 
of forces was suddenly broken by the yielding of 
some small particle in the woody tissues of the tree, 
and down it came. In all such cases there must be 
a moment of time when the upholding and down- 
pulling forces are just balanced; then the yielding 
of one grain more gives the victory to gravity. The 
slow minute changes in the tree, and in the stone 
wall, that precede their downfall, we do not see or 
hear; the sudden culmination and collapse alone 
arrest our attention. An earthquake is doubtless 
the result of the sudden release of forces that have 
been in stress and strain for years or ages; some 
point at last gives way, and the earth trembles or 
the mountains fall. 
It is the slow insensible changes in the equipoise 
of the elements about us that, in the course of long 
periods of time, put a new face upon the aspect 
of the earth. Rapid and noisy changes over large 
areas, which may have occurred during the geologic 
ages, we do not now see except in the case of an 
earthquake. It is the ceaseless activity, both chem- 
ical and physical, in the bodies about us, of which 
we take no note, that transforms the world. Atom by 
atom the face of the immobile rocks changes. The 
terrible demonstrative forces, such as electric dis- 
charges during a storm, which seem competent to 
106 
