Long before this, however, the screw propeller had proved so reliable and the advantage of its position below the water-line was so obvious that the Admiralty could no longer maintain its prejudice, and the warsloop _Rattler_ was built at Sheerness in 1843 and fitted with a screw propeller. Her displacement was 1078 tons. Her engines, of 437 indicated horse-power, had a spur gearing by which the revolutions of the screw were increased to four times those of the crank. The steamer _Alecto_ had paddle-engines of the direct-acting type, and of about the same power as those of the _Rattler_. The two vessels were made fast stern to stern with only a short distance between them to test the powers of their respective methods of propulsion, and although each did her best the screw boat towed the other at a speed of nearly 2¹⁄₂ knots. Of course a test of this sort could not demonstrate the superiority of one method over the other; all that it proved was that the _Alecto_ was less powerful than the _Rattler_. A similar contest took place in the English Channel in June 1849, between the screw corvette _Niger_ and the paddle-sloop _Basilisk_. The tug-of-war lasted an hour, and the _Niger_ towed the _Basilisk_ stern foremost 1·46 knots. These two vessels were very evenly matched in every respect, and the test in this case left no room for doubt as to which was the better method. The first screw-propelled vessel in the British Navy was the _Dwarf_, built as the _Mermaid_ by Messrs. Ditchburn and Mare at Blackwall in 1842, and as she attained at her trial the guaranteed speed of twelve miles an hour, the Admiralty fulfilled its promise and took her over and then renamed her. She was engined by Messrs. J. and G. Rennie. Her cylinders were vertical, of 40 inches diameter with 32 inches stroke, and the propeller was on their conoidal principle in which three blades are used, the surface of which, according to the specification, is “obtained by the descent of a tracer down the surface of a cone or conoid,” this giving an increasing pitch. The vessel was 130 feet long and of 164 tons measurement. Three years later she was used for a series of experiments with a variety of screw propellers. Of the many inventions brought under the notice of the Admiralty and of private shipowners, one which attained a considerable measure of success was the contrivance patented by Taylor and Davies in 1836, and known as a modified and improved form of Bishop’s disc engine. It was tried in a pinnace, the _Geyser_, built in 1842 by Rennie.