Sunday, September 16, 2012

The Ubiquitous Oh-Jive

The English language certainly contains some strange words, often with obscure etymological origins. Even everyday objects can be difficult to name. I came across the word ‘ogive’ last year. Not knowing its meaning, I looked it up, and now see ogives almost everywhere. (The more you know, the more you look and the more you see.)

An ogive is defined as the roundly tapered end of an object, be it two- or three-dimensional. Geometrically, it is formed from two parallel straight lines and two intersecting arcs whose radii are greater than the distance between the lines (Figure 48.1).

Figure 48.1: Diagrammatic representation of an ogive. The so-called ‘sharpness’, normally denoted as ‘E’, of this particular ogive is given by the ratio 120/100, i.e. 1.2. The greater the ratio, the sharper the tapered end.

Copyright © 2004 Securiger

Arguably the most common example is the Gothic (or ogival) Arch. Although widely considered to be a medieval structure, it is, in fact, Islamic. Europe is full of Gothic architecture, which often defines its most celebrated buildings, particularly cathedrals and churches.

Andalucía provides one of the most striking portrayals of this feature. Despite the Christian Reconquista of the 13th to 15th century, much of the original Islamic mudéjar style remained popular, and for good reason. Christians built their churches with ogives large and small, thus tacitly acknowledging the artistry of their Muslim predecessors. The finest testimony has to be Seville Cathedral – or, to give it its full title, El Catedral de Santa María de la Sede. This is the largest Gothic building – and third largest cathedral – in the world. It took the entire 15th century to construct, and an entire day for me to explore.

The cathedral’s ogives are too numerous to count, although its stained-glass windows and 15 exterior doors would be the best places to begin (Figure 48.2). Aesthetically, the ogive is a masterstroke; but that is, I admit, purely subjective. What would be impossible to deny, however, is one of its most important functional attributes: the ability to resist the enormous gravitational force of the wall above it. (Perhaps this indicates to us the origin of the word: obviare being the Latin verb ‘to resist’.) A frame with a horizontal header would be susceptible to stress fracture in the centre. The curves of an ogival arch, by contrast, help to dissipate an enormous load to its lateral supports. Those 9th century Muslims really were clever mathematicians.

Figure 48.2: Nested ogival arches above Seville Cathedral’s Door of the Prince

Copyright © 2012 Paul Spradbery

The ogival shape is not confined to architecture. Three-dimensional examples are commonly found in aerodynamics and ballistics. If an object is to move efficiently, through any medium, the shape of its ‘nose’ is crucial. Here, the streamlined ogive comes into its own. Bullets are ogival, as are submarine casings, Japanese rail locomotives and even suppositories. A wide range, for sure.

So, keep an eye out for ogives. As I say, they are everywhere – in churches especially (Figure 48.3), but even as garden features (Figure 48.4).

Figure 48.3: A delightful depiction of a 14th-15th century English church, complete with ogival-arched windows

Copyright © 2012 British Library Board

Figure 48.4: Not quite Seville Cathedral, but small-scale ogives can look good, too.

Copyright © 2011 Paul Spradbery

In case you were wondering, ‘ogive’ is pronounced ‘oh-jive’. I didn’t know, either!

Copyright © 2012 Paul Spradbery

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