Scientific American, June 14, 1884, page 373:
Opera by Telephone.
When the new opera "Lauriana" was produced recently for the first time, at the Lisbon Opera House, the King and Queen of Portugal were in mourning for the Princess of Saxony. The etiquette of courts prevented their royal highnesses from attending, and their despair thereat added to their grief at the loss of the Princess was like to have overwhelmed them. If Mohammed could not go to the mountain, the mountain must come to Mohammed. And so he brought the opera to their royal highnesses--by telephone.
Six microphone transmitters were placed about the front of the operatic stage in multiple arc. They were mounted on lead and soft rubber pedestals to prevent disturbance from the vibration of the building. Each transmitter was fed by three sets of batteries, which were switched on every twenty minutes in succession to keep on the current strength. There were receivers at the palace end for the use of the royal family, who thus heard the opera from beginning to end.