For the complete history of the discovery and introduction of the principle of the Electric Telegraph the reader is referred to the Society of Arts Journal (Nos. 348-9, vol. viii.), where it is stated that it is _half a century_, dating from August, 1859, since the first galvanic telegraph was made. "It was the Russian Baron Schilling's electro-magnetic telegraph which, without its being known to be his, was brought to London, and caused the establishment of the first practically useful telegraph lines, not only in Great Britain, but in the world." Dr. Hamel says: "The small sprout nursed on the Neva, which had been exhibited on the Rhine, and thence brought to the Thames, grew up here to a mighty tree, the fruit-laden branches of which, along with those from trees grown up since, extend more and more over the lands and seas of the Eastern hemisphere, whilst kindred trees planted in the Western hemisphere have covered that part of the world with their branches, some of which will, ere long, be interwoven with those in our hemisphere." The first telegraph line in England was constructed by Mr. Cooke from Paddington along the Great Western Railroad to West Drayton in 1838-39; and it must be remembered that it was in February, 1837, that Mr. Cooke first consulted Professor Charles Wheatstone, having previously visited Dr. Faraday and Dr. Roget, and on the 19th November, 1837, a partnership contract was concluded between Messrs. Cooke and Wheatstone. To the distinguished philosopher, Professor Wheatstone, the merit of the ingenious construction of the vertical-needle telegraph is due; whilst Mr. Cooke's name will always be associated with the practical establishment of the first telegraph lines in England. The first line in the United States, from Washington to Baltimore, was completed in 1844, being arranged and worked by Professor Morse. In British India, in April and May, 1839, the first long line of telegraph, twenty-one miles in length, and embracing 7000 feet of river surface, was constructed by Dr. (now Sir William) O'Shaughnessy. [Page 219] The construction of the electric telegraph may be considered under three heads: 1st. The Battery, _the motive power_. 2nd. The Wires, _the carriers of the force_. 3rd. The Instruments to be worked--_the bell_ and the _needle telegraph_. THE BATTERY. The construction and rationale of the batteries generally in use have been explained in another part of this work; those used for telegraphic purposes consist of one or more couples, of which zinc is one, the second being copper, silver, platinum, or carbon. Each couple is termed an element, and a series of such couples a _battery_.