American Scientist

To the Editors: 

Henry Petroski’s Engineering column in the November–December 2020 issue, Towers: Upright, Leaning, and Collapsed, got my attention. I was interested not only because of the descriptions of structural integrity degradation over long time periods but also because I live near a 20-meter leaning brick chimney. It was originally part of the heating system for a greenhouse that was crushed in a heavy snowfall a few years ago. The greenhouse lot is now used for boat and RV storage, but the chimney remains. 

The chimney stands alone about 20 meters east of a street that I travel nearly every day. It has a slight lean to the south that I measured to be 1.90 degrees. The appearance of the lean, however, is markedly affected by the direction I am traveling: When I’m driving north it appears to be perfectly vertical, but when I’m going south the lean is enhanced and gives the impression that it might fall over at any time! A somewhat unusual road layout with various curves and changes in slope is evidently the reason for this Escheresque visual trickery.  The interested reader may go to Google Earth to explore for himself the subtle street curves and elevation changes, including a sloping bridge. The chimney is located at 47° 42.00’ north latitude, 116° 56.958’ west longitude.

The mental processes going on in these sorts of situations is something I had not thought about until I read the Engineering column and decided to quantify the chimney effect. Thanks for taking this physicist out of his swim lane! 

Paul Temple
Post Falls, ID