Mr. Whishaw, in a paper communicated to the British Association in 1819, gave an ac count of the telegraphic systems followed in three countries, Great Prussia, and the United States. In Great Britain the wires are suspended on poles. The length of railway to which the system had been applied down to July 1849, was about 2000 miles ; and the cost was about 150/. per mile. In Prussia the telegraphic wires were suspended on the English system until the year 1814, since which date a new plan has been followed. The wires are coated with gutta percha, and laid along under ground, at a distance of about two feet beneath the surface, not only under railways, but under turnpike roads and towing paths. There are at each principal station two telegraphic machines, one colloquial and one printing. The length of Prussian telegraph to July 1819, was about 1500 miles, at a cost of about 401. per mile. In the United States the telegraphic line is formed by a single iron wire supported from post to post. It is car ried not only along railways, but across the open country. There were in July 1849, about 10,500 miles of American telegraph, at a cost of about 201. per mile.
Various improvements in electro-telegraphic machines have been patented from time to time by Messrs. Brett and Little, and other inventors ; hut those which seem most likely to be attended with important results relate to Submarine Telegraphs. It has been proved that wires may be so coated with gutta percha and other materials as to act under water. A tube so constructed has been carried under the see between Dover and Calais and the first communication by electric telegraph was made from Cape Grisnez to Dover on August 28, 1850. The length from Dover to Cape
Grisnez is 21 miles. The copper wire was of an inch in thickness, and was enclosed in a solid cylinder of gutta percha, l of an inch in diameter. The entire length of wire. was 25 miles, and its weight was 1 ton 2 cwt. 1 quarter 10i lbs. The weight of the gutta percha was 4 tons 7 ewts. 1 quarter 9 lbs.
Wherever the railway system has extended, there does the electro-telegraphic system find more or less of encouragement; and in the United States the telegraphic wires extend also over vast tracts of country where no rail ways are yet laid down. In respect to our own country, the contrivances of Messrs. Cooke and Wheatstone have hitherto been those most generally adopted ; but there is at the present time (May 1851) an attempt being made to form a new telegraphic company ; and if this attempt succeed, we shall probably see many new and efficient mechanical arrange ments adopted.
One of the most recent electromagnetic in struments, partaking of the nature of the electric telegraph in some of its features, is Mr. Shepherd's ingenious clock at the Indus trial Palace.
The experiments made in the British Chan nel have shewn that the submarine Telegraph is practicable ; and we shall probably see, ere long, the adoption of the system between Eng land and France, and between England and [reland. The proposed oceanic telegraph be Aveen England and America may well afford :o wait till the fruition of the less gigantic >chemes.