SCREW PROPELLER. From the time of Archimedes it has been known that a revolving screw may be made the means of 'raising water ; and it has also been known ;- that a peculiar resistance to the motion of a solid in a liquid results from the revolution of d a screw. A most important application of of this principle has been made within the last ? few years to steam navigation ; the screw steam • ships wholly depend upon. it.
• The first vessel fitted with a screw pro pellor was yacht, in which the screw was , fitted into the dead-wood, between the keel and the stern-post ; the screw consisted of a r helix, making but one revolution around a horizontal axis passing longitudinally through ; the ship; and it was put in motion by a steam ; engine. The absence of the ponderous , paddle wheels and paddle boxes of an ordinary r steamer greatly improves the sailing qualities of a screw•propelled vessel ; while the ar ; rangement of the machinery may be such as to render the vessel fax more commodious, ; and, if desired, to leave the upper decks open ; from end to end. The usual position of the I screw propeller, immediately before the stern post, does not appear either to be disadvan tageous to the application of the propelling power, or to interfere with the action of the rudder. An important use to which screw propellers have been advantageously applied, is as an auxiliary power, for occasional use during calms and contrary winds for vessels which are ordinarily moved by sails alone ; such auxiliary screws have been supplied to some of the Arctic ships.
The most notable screw steamer ever con structed was the Great Britain. It was 320 feet long by N broad. The burthen was about 3000 tons ; and the engines, consisting of four cylinders of 88 inches diameter by 72 inches stroke, were of 1000 horse power. It had a screw propeller lei feet in diameter, with six arms, mounted in the stern, and ca pable of being turned with great rapidity by the engine. After making four passages across the Atlantic, she was fitted with a new and much stronger propeller, weighing seven tons, of the same diameter as before, but consisting of only four arms or vanes. The subsequent disasters of this noble vessel are well known to most newspaper readers.
After varied experiments and trials a com mercial company took up the subject of Screw Steam Navigation ; and important results seem likely to follow. The company, formed in 1810, built two screw steamers, of 272 tons each for the Holyhead and Dublin trade. Two other vessels of 320 tons were afterwards added. In 1848 the company was remodelled, and commenced operations on a larger scale. Four screw steamers, from 450 to 500 tons, were built for the trade betWeen England and Constantinople, and performed the service waggon-jacks, &c., are sometimes formed by vary satisfactorily. In 1850 the company entered upon a contract with the admiralty, for a monthly mail to the Cape of Good Hope; the first screw steamer started on this service on Dee. 18, 1850, and returned to Plymouth on March 12, 1851 ; mid in respect to time and accommodation, the service is considered to have been amply performed.' The' com pany are now organizing arrangethents for an extension of the system to Mauritius, Ceylon, Madras, and Calcutta ; and should this be carried out, it is next contemplated to make a farther extension to the AUstralian 'colonies. It is calculated that screw steamers of 1700 tons burden and 300 horse power would reach Sydney from in 04 days ; and such vessels are now tieing built—There seems much probability that the recent perplexities concerning an Australian mail will be solved by the success of the screw steamers.
There are also screw steamers in the Royal Navy. Screw steamers have just been started from Glasgow to London—a distance of about 800 miles, whether taken north or south. In April of the present year the first screw' steamer started. from Glasgow to New York, an entirely new steam route. An American Company are building screw steamers large burden, expressly for the emigrant traffic from Liverpool to New York.—Such are the energetic proceedings which the success of the Screw Propeller has engendered.
See further in respect to steam navigation under STEAM VESSEL.
We may here mention that attempts bay been made to propel vessels by ejecting water from the stern. A propeller of this curious kind was patented by Mr. Purkis in 1849, and was tried on a, boat of largo size in the Thames.