APPENDIX. The Ionic Volute. The traditional explanation of the manner in which the Greeks set out the volute is given to us by Vitruvius, according to whom it was drawn by a series of arcs of circles gradually increasing in radius. The details of his scheme have been much discussed ; one of the latest theories of interpretation is that of Choisy, as given by M. Pontremoli in the volume " Didymes." The late Mr Penrose, feeling as a mathematician that such a method was only an approxima- tion to a true theoretic spiral, set out the theory that the volute was in fact drawn by means of a cord unwound from a central helix.* If the cord is unwound from a cylinder a spiral having equal intervals is produced, but this differs from the volute in starting quickly from the eye, and in having succeeding revolu- tions what we may call parallel to one another. If, however, the cord is unwound from a spiral or a cone an expanding volute results, which is almost exactly like the Ionic volute. Penrose thought further that the sunk eyes in the volutes were made to contain the helix from which the cord was unwound. Other reasons for the excavation of the eye have been given. Fig. 212. — Eyes of Volutes. A, Priene ; B, Ephesus.
- R.I. B.A. Jour., 1903, p. 21.
