The book Identification anthropométrique : instructions signalétiques is Alphonse Bertillon‘s guide for identifying criminal suspects.
These ear dimensions were one way you could make SUPER sure you got your man, and not somebody with similar features but totally the wrong ears.
At the time, the science was called anthropometry, and it was the ancestor to the biometrics used by surveillance computers to spot, for instance, specific faces on a crowded street.
Credit: Wellcome Library, London. Wellcome Images