Bunsen, thank you for rotating the image and making it local.

The Mac Chimney was an actual commercial product. The item pictured is not one of the commercial ones.

Back in the early 90s I was visiting my partner (girlfriend back then) at law school and she was still busy with some classes or something. I had read about the Mac Chimney, so I grabbed some balsa wood, poster board, glue, scissors and X-acto knife and voila, ventilation for the Mac 512KE here Mom had hand-me-downed to her.

There are balsa ribs sanded to conform to the top of the Mac under the poster board, giving the chimney sturdy support. Ah, here we go