As promised, here’s the answer to yesterday’s quiz.  As you see, once you see the trick, it’s quite easy.  The three battery/bell pairs are wired in series.  Buttons are wired to close the respective circuits.  The quiz appeared in the September, 1924, issue of Science and Invention magazine.

Here’s a bonus question:  How could you wire up another button that rings only bells 1 and 3?