33 mm. whilst the weather was dry between
May 9th and June 13th, and rose 1.91 mm, between September 7th and
19th of the same year, much rain having fallen during the latter
part of this time. During frosts and thaws the movements were
twice as great. These observations were made by my son Horace, who
will hereafter publish an account of the movements of this stone
during successive wet and dry seasons, and of the effects of its
being undermined by worms. Now when the ground swells, if it be
penetrated by cylindrical holes, such as worm-burrows, their walls
will tend to yield and be pressed inwards; and the yielding will be
greater in the deeper parts (supposing the whole to be equally
moistened) from the greater weight of the superincumbent soil which
has to be raised, than in the parts near the surface. When the
ground dries, the walls will shrink a little and the burrows will
be a little enlarged. Their enlargement, however, through the
lateral contraction of the ground, will not be favoured, but rather
opposed, by the weight of the superincumbent soil.
Distribution of Worms.--Earth-worms are found in all parts of the
world, and some of the genera have an enormous range. {41} They
inhabit the most isolated islands; they abound in Iceland, and are
known to exist in the West Indies, St.
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