Under these conditions, the undulatory currents necessary for the reproduction of speech were obtained in a mode analogous to that pointed out by Mr. Bell in his specification, that is, by the variations of resistance in the liquid layer interposed between the platinum wires of the transmitter; and their action, exerted on an electro-magnet, of which the armature was fixed on the diaphragm of the resonator, was produced under more favourable conditions than in Mr. Bell’s specification (see fig. 13), since that gentleman regards this arrangement (represented in fig. 14) as an important improvement on his first conception. The whole importance of the invention rests on the intervention of undulatory currents, which, as we have seen, are indispensable for the reproduction of speech, and it concerns us to know whether it was Mr. Bell or Mr. Gray who first declared their importance; for in both the specifications deposited on February 14, 1876, the use of undulatory currents was declared to be indispensable. Mr. Gray asserts that he had recognised their importance for the transmission of combined sounds as early as 1874; but Mr. Bell believes that the undulatory currents mentioned by Mr. Gray at that time were only currents analogous to those he had designated under the name of pulsatory currents, which we have represented in fig. 8. We have seen that since these currents only represent the abrupt elevations and depressions of intensity, they are unfit for the reproduction of articulate sounds, which, on the contrary, demand that the variations of intensity should result from successive efforts, in exact correspondence with all the inflections of the sonorous vibrations effected by the voice. Mr. Bell’s claim to priority on this question has been recognised by the American Patent Office, since he has been placed in possession of the patent. However this may be, Mr. Gray’s telephonic system was complete, and we see in it, as we have already said, the origin of the battery telephones, which have recently produced such important results. Let us now consider the relation which this system bears to Mr. Bell’s.