Trivial Tidbit from Modern Marvels

Ever wonder why sewer most manhole covers are round?

For the last few months, I've been working on and off on restoring the circular skylight in our old Victorian house. It involves dragging the ladder up a flight of stairs, wiggling through the access panel in the bathroom ceiling, balancing my way across the ceiling rafters because there is no floor, and doing all the work on the skylight in the dusty, hot, unventilated attic. Why? Because the darn window frame is round, and it won't fit through the hole in the ceiling so I can't lower it through to work on it in a better space.

Think back to high school geometry: though various shapes of manhole covers have been used over time (rectangular, trapezoidal, etc), round covers are the only ones that can't fall through the hole into the sewer passage below. My a-ha moment for the day.