EYE

cow's eye

cropped from a photo by ILRI

"Any homogeneous membrane which has holes in it will tend to rupture at the holes, unless the edges of the holes are reinforced by thickening.

The most familiar example of this principle at work is in the human face itself. Both eyes and mouth are surrounded by extra bone and flesh. It is this thickening, around the eyes and mouth, which gives them their character and helps to make them such important parts of human physionomy.

human eye

cropped from a photo by Dietmar Temps

A building also has its eyes and mouth: the windows and the doors. And following the principle which we observe in nature, almost every building has its windows and doors elaborated, made more special, by just the kind of thickening we see in eyes and mouths.

 

bull's-eye

photo by mirsasha

The fact that openings in naturally occurring membranes are invariably thickened can be easily explained by considering how the lines of force in the membrane must flow around the hole. The increasing density of lines of force around the perimeter of the hole requires that additional material be generated there to prevent tearing. (...) It is important to recognize that this stiffening is not only supporting the opening itself against collapse, but it is taking care of the stresses in the membrane which would normally be distributed in that part of the membrane which is removed.

 sketch from the book A Pattern Language

 

More general examples of frames as thickened edges exist all over the world.
They include
the thickening of the mud around the windows of a mud hut,
the use of stone edges to the opening in a brick wall because the stone is stronger,
the use of double studs around an opening in stud construction,
the extra stone around the windows in a Gothic church,
the extra weaving round the hole in any basket hut.

eyelet

(...) Do not consider door and window frames as separate rigid structures which are inserted into holes in walls. Think of them instead as thickenings of the very fabric of the wall itself, made to protect the wall against the concentrations of stress which develop around openings."

Christopher Alexander, Sara Ishikawa & Murray Silverstein
A Pattern Language
1977