What misconception about telephone circuits are they trying to address?
At least as I read it, he states the misconception fairly clearly:


  the sound produced at one end of a circuit actually travels over that
  circuit, in order to be heard at the other end.


His point is that the sound at one end of the circuit is converted to electrical signals by the microphone, then that resulting electricity travels through the circuit, and at the other end, sound is produced based on those electrical signals.

Yes, to most of us today, that probably seems pretty obvious--but in 1905 it wasn't nearly as widely understood. It appears that a fair number of people originally thought of the phone system as a more elaborate version of the old "telephone" kids made with a string between two tin cans.



That, of course, is not accurate at all.