it has a misty look--that is,
the motions elude the sight. It is easy to see that a shaking of this
kind is particularly calculated to disrupt any bodies which stand free
in the air and are supported only at their base.

In what we may call the natural architecture of the earth, the
pinnacles and obelisks, such as are formed in many high countries, the
effect of these shakings is destructive, and, as we have seen, even
the firmer-placed objects, such as the strong-walled cliffs and steep
slopes of earth, break down under the assaults. It is therefore no
matter of surprise that the buildings which man erects, where they are
composed of masonry, suffer greatly from these tremblings. In almost
all cases human edifices are constructed without regard to other
problems of strength than those which may be measured by their weight
and the resistance to fracture from gravitation alone. They are not
built with expectation of a quaking, but of a firm-set earth.

The damage which earthquakes do to buildings is in most cases due to
the fact that they sway their walls out of plumb, so that they are no
longer in position to support the weight which they have to bear. The
amount of this swaying is naturally very much greater than that which
the earth itself experiences in the movement. A building of any height
with its walls unsupported by neighbouring structures may find its
roof rocked to and fro through an arc which has a length of feet,
while its base moves only through a length of inches. The reader may
see an example of this nature if he will poise a thin book or a bit of
plank a foot long on top of a small table; then jarring the table so
that it swings through a distance of say a quarter of an inch, he will
see that the columnar object swings at its top through a much greater
distance, and is pretty sure to be overturned.

Where a building carries a load in its upper parts, such as may be
afforded by its heavy roof or the stores which it contains, the effect
of an earthquake shock such as carries the earth to and fro becomes
much more destructive than it might otherwise be. This weight lags
behind when the earth slips forward in the first movement of the
oscillation, with the effect that the walls of the building are pretty
sure to be thrust so far beyond the perpendicular that they give way
and are carried down by the weight which they bore. It has often been
remarked in earthquake shocks that tall columns, even where compo