Gray’s system 118 Phelps’s system 118 Cox Walker’s system 121 Trouvé’s system 121 Demoget’s system 124 Mac Tighe’s system 125 Modifications of telephonic organs 125 Righi’s system 126 Ader’s system 129 Jorgenson’s system 131 _EXPERIMENTS WITH THE TELEPHONE._ On the effects of voltaic and induced currents 132 On the effects of different telephonic organs 139 Edison’s experiments 140 Canestrelli’s experiments 142 Hughes’s and Roy’s experiments 143 Bréguet’s experiments 149 Luvini’s experiments 149 Warwick’s experiments 151 Experiments on the effects of mechanical shocks 154 Des Portes’ experiments 154 Thompson’s experiments 158 Theory of telephone 159 Nature of vibrations 160 Action of diaphragm 163 Action of magnet 167 Action of currents 169 Wiesendanger’s thermophone 171 _OTHER EXPERIMENTS WITH THE TELEPHONE._ D’Arsonval’s experiments 173 Eick’s experiments 175 Demoget’s experiments 176 Sensitiveness of telephone 179 Hellesen’s experiments 180 Zetsche’s experiments 181 _THE MICROPHONE._ History of microphone 182 Different systems 187 Hughes’s microphone 188 Gaiffe’s system 190 Carette’s system 191