The first edition of The Classical Orders of Architecture, published in 1985, set out to simplify the traditional method of proportioning the orders. By studying a number of historical treatises, a set of 'ideal' orders was developed. These were then proportioned, using the diameter of the column above its base as a module. Unlike previous examples, which commonly divided the module into 30 or 60 parts, proportions of the elements of the orders were then defined as decimal fractions of the module. The purpose of this method of proportioning was to avoid the use of unmanageable fractions, and at the same time to make it easy to use a calculator to determine dimensions.

This proved a popular system, particularly for those teaching the orders to students. Those hitherto baffled by the arithmetic of the orders could draw them with sufficient ease to be able to concentrate on the broader problems of the use of classical architectural grammar. The book in translation found a market in Germany, and - to my great joy - in Italy.

In his foreword Peter Hodson explains the genesis of this second edition, with its parallel 96-part orders added to the metric orders of the original. When he mooted the idea of a non-metric canon, the image I had was of the traditional school ruler, with 12 inches divided into eighths. I thought that perhaps the orders could be proportioned by means of major parts of the module (twelfths), divided into minor parts (eighths of twelfths, or ninety-sixths of the module). Chris Cotton undertook the initial task of converting all the proportions in the original plates into 96-part notation.

In fact these proportions did not prove amenable to subdivision into major and minor parts, and the second set of orders now published discards the method as cumbersome and irrelevant. Not surprisingly, the orders published in James Gibbs's Rules for Drawing the Several Parts of Architecture proved more amenable to 96-part notation than my decimal orders, presumably because of their fractional arrangement as well as the essentially feet-and-inches perspective of their author.

I set out with the intention of reproducing the original set of plates, amended to show the 96-part notation developed by Chris Cotton. However, because of the great influence ofJames Gibbs on American architecture of the 18 th century, an emphasis on Gibbs seemed appropriate. Calder Loth, of the Virginia Department of Historic Resources, was persuaded to write for the book the essay on Gibbs, and at the same time I agreed that my second parallel should be based not on the 'ideal' order developed for the first edition but on the orders set out in Gibbs's Rules.

In converting Gibbs's fractions (and fractions of fractions), I used computer-aided drafting for the initial setting-out of the orders, though the actual plates in the book were drawn by hand. (The first edition was of course completed before the use of CAD became universal.) In constructing the orders this way, I became aware of course that what had been found in 1985 to be appropriate for the pocket calculator is equally appropriate for the computer. Indeed, the computer is so good at dividing lengths into fractions that it is perfectly easy to draw the orders direct from Gibbs's Rules. To that extent, my reworking of Gibbs may seem superfluous, but it does have the advantage that it presents all the proportions of the orders according to a single comprehensible scale, as well as picking up one or two minor anomalies in Gibbs's original work. Moreover, its use makes it easy to avoid unduly complicated fractional dimensions.

Moreover, the use of CAD proved a powerful asset both in checking the arithmetic of the new proportions, and in solving two hitherto somewhat intractable problems, the setting-out of the volute and the scotia. The volute is a stern test of draftsmanship because of its dependence on a high level of accuracy in striking the centres of its component quadrants. Finding the centre of the lower arc of the scotia is a trigonometrical puzzle that Cotton has solved but that I in the end preferred to circumvent.

The book therefore offers readers (on both sides of the Atlantic) a choice of two sets of orders. The variations between them are not for the most part great. But in one significant respect Gibbs (and Palladio) depart from the models I chose for proportioning my orders. This is in the proportion of entablature to column in the 'major' orders - Ionic, Corinthian and Composite. Gibbs's deliberate reduction of the scale of the entablature in these orders produces a lighter balance, which is more apparent in a building as a whole than in its constituent orders. Some may find this preferable to the emphasis on the entablature prescribed by Chambers and others, which I adopted for my original 'ideal'.

In all respects the 96-part orders are shown in the same way as those with 100 parts.

In presenting this book I acknowledge gratefully the advocacy of Peter Hodson, the painstaking re-calculation of the proportions by Chris Cotton, and the elegant contribution of Calder Loth, as well as the efforts of my colleagues Julia Nicholson and John Bridges, for transcribing my manuscript scribbling and converting my manual efforts into material suitable for the age of the computer.

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