No one can examine the set of receiving instruments collected in Fig. 46 without being struck with the extraordinary similarity of design which pervades the entire series. In every one of the set there is an electro-magnet, the function of which is to set an armature[52] into vibration by attracting it with a variable force. In every one the armature is of a material capable of magnetic induction; that is to say, iron, steel, or equivalent material. In every one of them the armature is either elastically mounted, or is in itself elastic. In every one of them (save only the two quite recent forms, _F_ and _I_, which were intended not to speak, but to emit only one fixed musical note) there is an extended surface (either a sound-board or a tympanum) to communicate the vibrations to the air. Lastly, every one of these forms, when connected with the line through which the telephonic currents are being transmitted, is perfectly capable of reproducing articulate speech. But the inventor who had the genius to discover all these essential points, and to combine them in an instrument, and to use it to reproduce articulate speech, is surely the true inventor of the system. The inventor of the system embodying these essential points was Philipp Reis. FOOTNOTES: [49] See Prescott’s ‘Speaking Telephone,’ p. 158. [50] ‘British Patent,’ No. 1874, of the year 1876 (dated 4th May). [51] Prescott, ‘Speaking Telephone,’ p. 203. [52] Yet Bell’s claim (British Patent Specification) runs: “I claim the production of any given sound or sounds from the _armature_ of the receiving instrument.” APPENDIX IV. ON THE DOCTRINE OF UNDULATORY CURRENTS. “_In this Specification the three words ‘oscillation,’ ‘vibration’ and ‘undulation,’ are used synonymously._”--Graham Bell, U.S. Patent, No. 174,465, filed Feb. 14, 1876. In the preceding appendices it has been demonstrated that all that is essential in both transmitter and receiver of a Telephonic system was to be found existing in 1863 in the Telephone of Reis. There yet remains to be met the _doctrinaire_ objection that as Reis never explicitly mentions an undulatory current as distinguished from an intermittent one, he never intended to use such a current. This objection is advanced only by those persons who have committed themselves to the idea that speech cannot be transmitted by a transmitter which opens and closes the circuit.