We learn by the “Paducah (Ky.) Pennant,” that a great telegraph cable was laid across the Ohio River at that place, on the 26th inst. -by Tal. P. Shaffner, Secretary of the American Telegraph Confederation, assisted by J. B. Sleeth, Mechanical Engineer. It is composed of a large iron wire, covered with three coatings of gutta percha, making a cord of about five-eigths of an inch in diameter. To protect this from wear, and for security of insulation, there are three coverings ol strong Osraburg, saturated with an elastic composition of gutta percha, and around this are eighteen large iron wires, drawn as tight as the wire will bear, and the whole is then spirally lashed together with another large wire, passing around at every J of an inch.— The whole forms a cable of near two inches in diame'er. This wire conducts ,the electric current beneath the bed of the Ohio for a distance of 4,200 feet, and is said to be the longest telegraph cable in the Union. The company was much troubled before on account of unsuccessful efforts to cross the river with the wire, and secure it against accident. It is believed that this cable will effect a great saving to the company, and at the same time obviate ? much trouble.