osition.
It used to be regarded as one of the standing rules of my old
profession, that the 'broad bed of a stone' is the best, and should be
always laid 'below.'" "A good rule for the land," replied Mr. Bremner,
"but no good rule for the sea. The greatest blunders are almost always
perpetrated through the misapplication of good rules. On a coast like
ours, where boulders of a ton weight are rolled about with every storm
like pebbles, these stones, if placed on what a workman would term their
best beds, would be scattered along the shore like sea-wrack, by the
gales of a single winter. In setting aside the prejudice," continued Mr.
Bremner, "that what is indisputably the best bed for a stone on dry land
is also the best bed in the water on an exposed coast, I reasoned
thus:--The surf that dashes along the beach in times of tempest, and
that forms the enemy with which I have to contend, is not simply water,
with an onward impetus communicated to it by the wind and tide, and a
reactive impetus in the opposite direction,--the effect of the backward
rebound, and of its own weight, when raised by these propelling forces
above its average level of surface. True, it is all this; but it is also
something more. As its white breadth of foam indicates, it is a subtile
mixture of water and _air_, with a powerful _upward_ action,--a
consequence of the air struggling to effect its escape; and this upward
action must be taken into account in our calculations, as certainly as
the other and more generally recognized actions. In striking against a
piece of building, this subtile mixture dashes through the interstices
into the interior of the masonry, and, filling up all its cavities, has
by its upward action, a tendency to _set the work afloat_. And the
broader the beds of the stones, of course the more extensive are the
surfaces which it has to act upon. One of these flat flags, ten feet by
four, and a foot in thickness, would present to this upheaving force, if
placed on end, a superficies of but _four_ square feet; whereas, if
placed on its broader base, it would present to it a superficies of
_forty_ square feet. Obviously, then, with regard to this aerial
upheaving force, that acts upon the masonry in a direction in which no
precautions are usually adopted to bind it fast,--for the existence of
the force itself is not taken into account,--the greater bed of the
stone must be just ten times over a worse bed than its lesser one; and
on