The length of line through which Morse could work his apparatus was an important point to be determined, for it was known that the current grows feebler in proportion to the resistance of the wire it traverses. Morse saw a way out of the difficulty, as Davy, Cooke, and Wheatstone did, by the device known as the relay. Were the current too weak to effect the marking of a message, it might nevertheless be sufficiently strong to open and close the circuit of a local battery which would print the signals. Such relays and local batteries, fixed at intervals along the line, as post-horses on a turnpike, would convey the message to an immense distance. 'If I can succeed in working a magnet ten miles,' said Morse,'I can go round the globe. It matters not how delicate the movement may be.' According to his own statement, he devised the relay in 1836 or earlier; but it was not until the beginning of 1837 that he explained the device, and showed the working of his apparatus to his friend, Mr. Leonard D. Gale, Professor of Chemistry in the University. This gentleman took a lively interest in the apparatus, and proved a generous ally of the inventor. Until then Morse had only tried his recorder on a few yards of wire, the battery was a single pair of plates, and the electro-magnet was of the elementary sort employed by Moll, and illustrated in the older books. The artist, indeed, was very ignorant of what had been done by other electricians; and Professor Gale was able to enlighten him. When Gale acquainted him with some results in telegraphing obtained by Mr. Barlow, he said he was not aware that anyone had even conceived the notion of using the magnet for such a purpose. The researches of Professor Joseph Henry on the electro-magnet, in 1830, were equally unknown to Morse, until Professor Gale drew his attention to them, and in accordance with the results, suggested that the simple electro-magnet, with a few turns of thick wire which he employed, should be replaced by one having a coil of long thin wire. By this change a much feebler current would be able to excite the magnet, and the recorder would mark through a greater length of line. Henry himself, in 1832, had devised a telegraph similar to that of Morse, and signalled through a mile of wire, by causing the armature of his electro-magnet to strike a bell. This was virtually the first electro-magnetic acoustic telegraph.[AMERICAN JOURNAL OF SCIENCE.]