CROFT.
For nearly three-quarters of a century after its introduction the Tracery of windows contained forms in which that simplest of all Geometrical figures, the Circle, was principally conspicuous: and although, in the latter part of this Period, the Circle does not obtain the same prominent place, in the centre of the window-head, and as the principal feature of the design, that is generally allotted to it in the earlier examples, yet the important part that it bears in the construction of the design of even the whole of these later examples, fully justifies the application of the term, already pretty generally in use, to this class of windows; and entitles us to call this Period after that figure, and "par excellence," the GEOMETRICAL PERIOD.
HOWDEN.
At the close of this Period a feature began to make its way into the subordinate parts of the tracery, which had already shown itself for some time previously in the mouldings, and which eventually exercised a most important influence on the Architecture of the next half-century.
This feature is the curve which mathematicians call the curve of contra-flexure, and which is known amongst architecturalists as the Ogee.
