at only three architects are now
properly competitors for the honour of this great employment; by two of
whom are proposed semicircular, and by the other elliptical arches.

The question is, therefore, whether an elliptical or semicircular arch
is to be preferred?

The first excellence of a bridge, built for commerce, over a large
river, is strength; for a bridge which cannot stand, however beautiful,
will boast its beauty but a little while: the stronger arch is,
therefore, to be preferred, and much more to be preferred, if, with
greater strength, it has greater beauty.

Those who are acquainted with the mathematical principles of
architecture, are not many; and yet fewer are they who will, upon any
single occasion, endure any laborious stretch of thought, or harass
their minds with unaccustomed investigations. We shall, therefore,
attempt to show the weakness of the elliptical arch, by arguments which
appeal simply to common reason, and which will yet stand the test of
geometrical examination.

All arches have a certain degree of weakness. No hollow building can be
equally strong with a solid mass, of which every upper part presses
perpendicularly upon the lower. Any weight laid upon the top of an arch,
has a tendency to force that top into the vacuity below; and the arch,
thus loaded on the top, stands only because the stones that form it,
being wider in the upper than in the lower parts, that part that fills a
wider space cannot fall through a space less wide; but the force which,
laid upon a flat, would press directly downwards, is dispersed each way
in a lateral direction, as the parts of a beam are pushed out to the
right and left by a wedge driven between them. In proportion as the
stones are wider at the top than at the bottom, they can less easily be
forced downwards, and, as their lateral surfaces tend more from the
centre to each side, to so much more is the pressure directed laterally
towards the piers, and so much less perpendicularly towards the vacuity.

Upon this plain principle the semicircular arch may be demonstrated to
excel in strength the elliptical arch, which, approaching nearer to a
straight line, must be constructed with stones whose diminution
downwards is very little, and of which the pressure is almost
perpendicular.

It has yet been sometimes asserted by hardy ignorance, that the
elliptical arch is stronger than the semicircular; or in other terms,
that any mass is more strongly sup