whether it rested upon them, or the vibrating fork was held above them. These substances were not adapted for transmitting the sound of the voice. These were all laid aside, and the sounding instrument was held directly above the pole of the magnet: the sound was clearly heard, although there was nothing but air between the end of the magnet and the tuning-fork. The sound was perhaps less intense when the tuning-fork was held directly above the pole, than when it was at the end of the magnet. I next tried if my voice could be heard with this arrangement. The result was rather doubtful, but I think that some action must have taken place, for the tuning-fork was heard when it was simply vibrated near the pole. The effect of the voice can only have differed in the degree of intensity: it was too faint to be heard at the other extremity. I repeated these effects; I assured myself of them, and I succeeded in transmitting sounds distinctly on the pole without a disk, and, on the other hand, by applying my ear to the instrument, I was able to hear distinctly all that was said, although there was no disk.’ [13] These are his own words: ‘The articulation produced from the instrument was remarkably clear, but its great defect consisted in the fact that it could not be used as a sending instrument, and thus two telephones were required at each station, one for transmitting and one for receiving spoken messages.’ [14] These carbons are made by heating, in a temperature gradually raised to white heat, fragments of deal of a close fibre, which is enclosed in an iron tube or box hermetically sealed. [15] Mr. Willoughby Smith varied this experiment by placing a packet of silk threads coated with copper on the disconnected ends of the circuit, which were arranged at right angles with each other. Under these conditions the instrument became so sensitive, that the current of air produced by a lamp placed above the system, caused a decided crackling noise in the telephone. [16] Mr. Hughes observes on this subject that carbon is a valuable material for such purposes, since it does not oxidise, and its effects are greater when combined with mercury. He takes the prepared charcoal used by artists, brings it to a white heat, and suddenly plunges it in a bath of mercury, of which the globules instantly penetrate the pores of charcoal, and may be said to metallise it. He also tried charcoal coated with a deposit of platinum, or impregnated with chloride of platinum, but this was not more successful than the former method. If the charcoal of fir-wood is brought to a white heat in an iron tube, containing tin and zinc, or any other metal which readily evaporates, it is metallised, and is adapted for use if the metal is subdivided in the pores of charcoal and not combined with it. When iron is introduced into carbon in this way it is one of the most effective metals. The charcoal of fir-wood, in itself a bad conductor, may thus acquire great conducting power.