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is farthest from its attachment; whence it follows that d being
equally distant from f, e .....
If the centering of the arch does not settle as the arch settles,
the mortar, as it dries, will shrink and detach itself from the
bricks between which it was laid to keep them together; and as it
thus leaves them disjoined the vault will remain loosely built, and
the rains will soon destroy it.
7
86.
ON THE STRENGTH AND NATURE OF ARCHES, AND WHERE THEY ARE
STRONG OR
WEAK; AND THE SAME AS TO COLUMNS.
That part of the arch which is nearer to the horizontal offers least
resistance to the weight placed on it.
When the triangle a z n, by settling, drives backwards the 2/3 of
each 1/2 circle that is a s and in the same way z m, the reason
is that a is perpendicularly over b and so likewise z is above
f.
Either half of an arch, if overweighted, will break at 2/3 of its
height, the point which corresponds to the perpendicular line above
the middle of its bases, as is seen at a b; and this happens
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