LETTERS TO THE EDITORS The Perfect Dome To the Editors: Henry
Petroski’s article “Arches and Domes” (March–April) reminded me
that the earliest masonry domes were probably snow houses or
igloos, rather than highly decorated houses of worship. The
igloo is not a hemisphere, which would collapse as the snow
compresses and the sides bulge out. Instead, igloos follow a
more complex curve called a catenary. Catenary, which derives
from the Latin word for chain, describes the curve taken by a
hanging chain that is held at both ends. As it compresses, an
igloo retains its catenary shape and simply becomes shorter.
When it gets too short, it is time to build a new igloo. The
igloo in the photo (at right) was built in 1970 as a
demonstration by Inuit of Pond Inlet, Nunavut, Canada. Once it
was complete, I tested its strength with a device that measures
the snow’s cohesion and internal friction. Based on the results,
I calculated that an igloo could have a maximum diameter of 10
meters. An igloo of approximately that d