Sunday, October 3, 2021

Geometry of the Old First Church Fanlight



This is the fanlight over the main door to the Old First Church, built in 1803-5 in Bennington, Vermont. Lavius Fillmore was the Master Builder; Oliver Abel, his Master Carpenter, and Asa Hyde, the Joiner and carver.  

 The fanlight design consists of 2 parts: the 'scallops' around the curve and the 'leaves' coming up from the base. It is simple, graceful.

How was it laid out? In 2012 - when I first wrote about this fanlight - I knew the geometry for the scallops around the curve - expanded daisy wheels on the horizontal and the vertical axis. 

The 3 leaves below the scallops?  I was lost.

Laurie Smith - English timber framer, historian, geometer, the most knowledgeable person I know about the use of circle geometry in medieval design and construction - provided an answer.
Here was our geometry for the fan light in 2012.  Now, in 2021, I think it is probably not how Lavius Fillmore laid out the pattern. 

I post it because we are teaching ourselves. We are constantly learning more about how to use Practical Geometry (or 'Architectural Geometry'). One solution is not the only one. 

A square can be  derived from a circle in many ways - as can a 3/4/5 rectangle - both done using only a compass, straightedge and a marking tool. To see how the geometry can be followed and bring different designers seeing different paths, arriving at the same solution, is valuable.



 The  circle, its 6 points around the circumference laid out by the radius of the circle, is set on a line which defines the shape of the fan light.



The circle is surrounded by 6 circles which have their centers on the 6  points. The center pattern is a daisy wheel with 'petals'.

 The circles expanded.



This set of circles around the original circle adds petals 
to the exterior of the first circle. Add the fanlight shape and the petals  become scallops around the arc of the fanlight.





 Rotate the circles 15*  - or 1/2 a petal - and the fanlight's scallops' locations change.

Overlapped, the daisy petals create the double scallops around the Old First Church fanlight. See the photograph above.



The overlapped petals are also the pattern of the 'leaves' in the  fanlight: too big, not in the right location, but crossed as are the leaves. 

This pattern is much easier to layout than the geometry in the next 5 drawings. I include those drawings to show another way which is equally valid but more complex. 

However, as I have explored the Old First Church geometry over the past 10 years,  I have gained a sense of how Lavius Fillmore designed. I do not think he used the sequences laid out here. He understood what the simple act of turning an expanded circle on its axis could create. 

The simple solution is here : 



Here is how the leaves could have been added. These steps are our 2012 solution.

Add regulating lines from the center of the circles to the second ring of circles and center lines in the petals.


Connect the center points of the scallops to each other. Where they cross the petals is the center of the small circles which form the leaves. 







The radius of the circles is the distance from the center of the petal to the scallop.









I've drawn it in red to make it more visible. It is a complex layout for a seemly quiet, unassuming design.

This pattern was drawn at about 3/8" = 1'-0".  A scale of 1"=1'0" might have been easier. However it would still be tiny here on the page. For clarity I left out the overlapping scallops.



my drawing in 2012:

The real fanlight was laid out full scale - 5+ feet across -  on a framing table or floor. The proposed design sketch would have been studied, the arcs drawn with a compass using chalk or charcoal, the lines checked, redrawn, the points pinned.  Finally, when the regulating lines were erased, the simple, clean design was visible.

I would like to have been there, listening, watching. as the men drew this.  I think they were pleased as they derived the pattern and settled on a design.  It's not structural at all. It's one of the first things you see, an introduction to the church. It's also their signature.

Then -  I realized that this derivation is not simple enough. 

My Addendum, my next post, is my current solution, my current understanding of how Lavius Fillmore, Oliver Abel, and Asa Hyde designed the fanlight.

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