There is a useful test of how hard something is to make: look at what people did before they had it.
Before metal needles, sewing was done with points made…
There is a tool so ordinary that almost nobody has considered how it works, and the answer turns out to be more particular than expected.
The obvious model is a…
There is a common assumption that sealing a letter was about privacy, and it misses what the object was for.
A seal provides no privacy whatsoever. Anybody determined to read…
There is a class of object that has to work with nobody supervising it, in public, permanently, and postboxes are among the clearest examples.
Before they existed, a letter had…
There is a reason water clocks were difficult and sand timers were easy, and it comes down to a surprising difference between liquids and piles of small solid grains.
A…
There is a question about weathervanes that catches almost everybody out, and it concerns which way the pointer faces.
The natural assumption is that the arrow shows where the wind…