In all the earlier experiments of Professor Bell, he employed galvanic batteries to produce the current; but these were afterwards dispensed with, and their place supplied by permanent magnets. With this improved arrangement, sounds were conveyed through a wire to a distance of a hundred and forty-three miles, from Boston to North Conway in New Hampshire. Last February a lecture was delivered, on the subject of Telephony, by Professor Bell at Salem, and was audible, word for word, at Boston. In order to shew that the transmission is equally available in both directions, provided the proper apparatus is at both ends, the lecture from Salem to Boston was followed on the same evening by singing and speech-making from Boston to Salem. From the patent specifications and from the descriptions in American scientific journals, it would appear that a phonographic reporter of some skill is needed, to translate the audible sounds into words and write them down. We must first comprehend, however, the mode in which the sonorous transmission through the wire is brought about; for this it is which really constitutes the principle of the telephone. Ordinary telegraphic coils of insulated wire are applied to the poles of a powerful compound permanent magnet; and in front of these is a thin vibrating diaphragm or membrane, with a metallic contact-piece cemented to it. A mouth-piece or trumpet mouth, fitted to collect and intensify waves of sound, is placed near the other surface of the diaphragm. It is known that the motion of steel or iron in front of the poles of a magnet creates a disturbance of electricity in coils surrounding those poles; and the duration of this current will coincide with the vibratory motion of the steel or iron. When, therefore, the human voice (or any other suitable sound) impinges through the tube against the diaphragm, the diaphragm itself begins to vibrate, and the contact-piece awakens (so to speak) electrical action in the coils of wire surrounding the poles of the magnet; not a current, but a series of undulations, something like those produced by the voice in the air around us. The undulations in the coil produce a current in the ordinary telegraph wire with which it is placed in connection. A similar apparatus at the other end is hereby set in action, but in reverse order; that is, the wire affects another coil, the coil another diaphragm, and the diaphragm another tube, in which the sounds are reproduced in audible vibrations.