John Napier’s Cockerel

In my post from Sunday, I talked about base rates and how police investigative techniques can go wrong. I specifically focused on testing methods for drug residue, which are not always as accurate as you might hope.

On an interestingly related note, today I was reading the chapter on logarithms from “In Pursuit of the Unknown: 17 Equations That Changed the World” (one of my math books I’m reading this year).  It was discussing John Napier, a Scottish mathematician who invented logarithms in the early 1600s.  Napier was an interesting guy….friend of Tycho Brahe, brilliant mathematician, and possible believer in the occult. For reasons possibly having to do with one of  those last two, he apparently carried a black cockerel (rooster) around with him a lot.

It’s actually not clear if he really was involved in the occult, but he did tell everyone he had a magic rooster. He used it to catch thieves.  Here’s what his strategy was:


No idea what the base rate was here, or if it would hold up in court today….but maybe something to consider if the budget gets cut.

(Special thanks to the Shakespeare translator for helping me out a bit on this one).