There was an electrician doing work down the block... he was a nice old guy and tested with his fingers... he told us kids not try it... only electrician I even met that did this... it was back in the 60's so he would have learned the trade around the time the book was published.
Off topic... my CPA collects old how to books... one dated 1922 describes how to wire your new home and save... about 30 pages and well illustrated and east to read... soldering, knob and tube and Edison Fuses... it did admonish while saving on labor was fine... the homeowner should not skimp on convenience outlets... saying every room must have at least one.
Also plentiful light switches are the mark of a job well done instead of pull cord fixtures.