"And in imagination she saw the judge's old hands put the black cap on his head and begin to pronounce sentence."
Hangman's noose
Creative Commons Attribution Share AlikeHangman's noose - Credit: Chris 73

In English courts of law, the judge's black cap was a nine-inch square of black silk that the judge would place on his head prior to pronouncing the death sentence on a convicted prisoner. After doing so he would say, "The sentence of this court is that you be taken to a place of execution and that there you be hanged by the neck until you are dead. And may the Lord have mercy on your soul."

A history of judicial hanging in Britain may be found here. The death penalty was effectively ended in Britain in 1965, and formally abolished in 1999.