On this day in 1891 Ernest Jules Pierre was granted the patent for Bi-Telephone. U.S. Patent No. 454,138.
This invention relates to an improvement in telephone-receivers, and has for its objects, first, to produce an apparatus for containing the operating parts of telephone-receivers, which shall be light enough to be carried while in use on the head of the operator, and second, and improved means for securing the same in place.