five* and fevgn arches * , that crofs the canal, are extremely
light and beautiful to the eye, but the plan on which they are
ufually conftruflted does not imply much ftrength. Each
ftone, from five to ten feet in length, is cut fo as to form a feg-
ment of the arch, and as, in fuch cafes, there is no key-ftone,
ribs o f wood fitted to. the convexity o f the arch are bolted
through the Hopes by iron bars, fixed fail into the folid parts o f
the bridge. Sometimes, however, they are without wood, and
the curved ftones are morticed into long tranfverfe blocks o f
ftpne, as in the annexed plate, which was drawn with great
accuracy by Mr. Alexander.
In this Plate,
No. i . Are .ftones cut to. the curve o f the arch i o feet long,
2. A n immenfe ftone, % feet fquare, o f the whole
depth o f the arch.
3; Curved ftones, 7 feet long.
4. Ditto, 5 feet>
5. Ditto, 3Í feet.
6. Ditto, 3 feet-
7. Ditto, 3 feet*
8.8. Stones fimilar to No. 2. being each one entire
piece running through the bridge, and intended;
it would feem, to bind the fabric together as the
pillars 9.9. are morticed into them.
Thefe are, however, other arches wherein the ftones are fmaller
aud pointed to a centre a.s in ours. I have underftood from,
* A bridge with junety-one arches will be noticed in ajfubiequent chapter.
the