The importance of Mr. Gray’s, as of La Cour’s inventions, depends, however, far more on the way in which they increase the message-bearing capacity of telegraphy than on their power of conveying airs to a distance. At the Philadelphia Exhibition, Sir W. Thomson heard four messages sounded simultaneously by the Gray telephone. The Morse alphabet was used. I have mentioned that in that alphabet various combinations of dots and dashes are used to represent different letters; it is only necessary to substitute the short and long duration of a note for dots and dashes to have a similar sound alphabet. Suppose, now, four tuning-forks at the transmitting station, whose notes are _Do_ [Illustration], _Mi_, _Sol_, and _Do_ [Illustration], or say _C_, _E_, _G_, and _C_´, then by each of these forks a separate message may be transmitted, all the messages being carried simultaneously by the same line to separate sounding reeds (or forks, if preferred), and received by different clerks. With a suitable key-board, a single clerk could send the four messages simultaneously, striking chords instead of single notes, though considerable practice would be necessary to transform four verbal messages at once into the proper telephonic music, and some skill in fingering to give the proper duration to each note. Lastly, we come to the greatest achievement of all, Professor Graham Bell’s vocal telephone. In the autumn of 1875 I had the pleasure of hearing from Professor Bell in the course of a ride—all too short—from Boston to Salem, Mass., an account of his instrument as then devised, and of his hopes as to future developments. These hopes have since been in great part fulfilled, but I venture to predict that we do not yet know all, or nearly all, that the vocal telephone, in Bell’s hands, is to achieve. It ought to be mentioned at the outset that Bell claims to have demonstrated in 1873 (a year before La Cour) the possibility of transmitting several messages simultaneously by means of the Morse alphabet.