ll be
different, and consequently, unless a very regular system of planning is
adopted, the piers will not be exactly opposite the solid portions of
the aisle walls, and consequently the centres of the arches will be out
of line with the centres of the windows. Again, it may be that, by
accident or design, the backing for the responds may project more on one
side of the nave than on the other, at either or both ends. The result
will be that the piers of one arcade will be out of line with those of
the arcade opposite. That discrepancies of this kind were sometimes the
result of intention cannot be denied; but there is generally some
practical reason to be found for the intention, and the discrepancies
themselves were a _pis aller_ which the builders would have avoided, if
they could. That deliberate irregularity with which medieval masons are
sometimes credited is a fancy, which careful consideration of the
circumstances will dispel.

Sec. 46. Hitherto we have spoken of the aisled nave as though both aisles
were planned at one and the same time. This, however, was by no means
always the case. At Gretton in Northamptonshire, the north aisle was
built soon after the beginning of the twelfth century: the south aisle
followed twenty or thirty years later. The north arcade at Northallerton
is of massive twelfth century work, with rounded arches: the south
arcade was added in the thirteenth century, and has slender columns with
pointed arches. In such cases, the north aisle may have been built
first, to avoid interference with the burial ground south of the church.
Very often only one aisle was added. The little church of Whitwell,
Rutland, has a south aisle, added in the fourteenth century, with a
chapel at its east end. No north aisle was built: but a drain in the
north wall of the nave shows that there was a third altar against the
north side of the rood screen. Usually, when one aisle was built long
after another, the spacing of the new arcade was made to correspond with
that of the old. If the old arcade had heavy twelfth century columns,
the new one, with its lighter columns, would have broader arches. But it
sometimes happens that the old spacing was disregarded, for very good
reasons. The north arcade of Middleton Tyas church, in north Yorkshire,
consists of six bays: the columns are heavy, the arches low and round
headed, and very narrow. The interior of the church must have been very
dark; and the builders of the so