les, set close to each
other in varied but not irregular relations, is thrown, like a necklace
of precious stones, round the apse and along the ends of the aisles;
each side of the apse taking, of course, as many triangles as its width
permits. If the reader will look back to the measures of the sides of
the apse, given before, p. 42, he will see that the first and seventh of
the series, being much narrower than the rest, cannot take so many
triangles in their band. Accordingly, they have only six each, while the
other five sides have seven. Of these groups of seven triangles each,
that used for the third and fifth sides of the apse is the uppermost in
Plate III.; and that used for the centre of the apse, and of the whole
series, is the lowermost in the same plate; _the piece of black and
white marble being used to emphasize the centre of the chain_, exactly
as a painter would use a dark touch for a similar purpose.

Sec. XXII. And now, with a little trouble, we can set before the reader,
at a glance, the arrangement of the groups along the entire extremity of
the church.

There are thirteen recesses, indicative of thirteen arches, seen in the
ground plan, fig. 2, Plate I. Of these, the second and twelfth arches
rise higher than the rest; so high as to break the decorated band; and
the groups of triangles we have to enumerate are, therefore, only eleven
in number; one above each of the eleven low arches. And of these eleven,
the first and second, tenth and eleventh, are at the ends of the aisles;
while the third to the ninth, inclusive, go round the apse. Thus, in the
following table, the numerals indicate the place of each entire group
(counting from the south to the north side of the church, or from left
to right), and the letters indicate the species of triangle of which it
is composed, as described in the list given above.

6. h. i. h. g. h. i. h.
5. b. c. a. d. a. c. b. 7. b. c. a. d. a. c. b.
4. b. a. b. c. a. e. a. 8. a. e. a. c. b. a. b.
3. b. a. b. e. b. a. 9. a. b. e. b. a. b.
2. a. b. c. 10. a. b. c. b.
1. a. b. c. b. a. 11. b. a. c. f. a. a.

The central group is put first, that it may be seen how the series on
the two sides of the apse answer each other. It was a very curious freak
to insert the triangle e, in the outermost place _but one_ of both the
f