ADMIRALTY EXPERIMENTS. 



and screw-vessel set stern to stern push one another instead of 

 pulling one another, the paddle-vessel preponderates, whereas, if 

 they pull, the screw-vessel preponderates. These circumstances 

 seem to show that the power of a screw-vessel to tow a paddle- 

 vessel astern, when the two are tied together, does not arise from 

 any superior tractive efficacy of the screw itself, hut is due to the 

 centrifugal action of the screw, which raises the level of the water 

 at the stern, so that the vessel gravitates down an inclined plane.* 



75. The first experiments tried by the Admiralty with the 

 screw-propeller were made in 1840-41 ; and in the next three 

 years, 1842-44, eight screw vessels were built. This number was 

 augmented by twenty-six in 1845. In 1848 there were not less 

 than forty-five government screw-steamers afloat ; and since that 

 time, and more especially since the commencement of the war 

 with Russia, the increase of the screw-steam navy has gone on at 

 a rate which justifies the conclusion that ere long no vessel of 

 war, of whatever class, in the British navy will be unprovided 

 with the power, to a greater or less extent, of steam propulsion. 



76. In a government official report of the results of various trials 

 of the performance of screw-steamers, dated so far back as May 

 1850, before that propeller had yet reached its present state of 

 perfection, it is stated as then highly probable that fine sailing 

 vessels, fitted with auxiliary screw-power, would be found able, 

 if not to rival, at least to approach, full-powered and expansively 

 acting steam-ships, in respect of their capability of making a long 

 voyage with certainty and in a reasonably short time. 



"Another application of the screw, although inferior in general 

 importance to its application as a propeller to ordinary ships," 

 says the same report, "is certainly deserving of more attention 

 than is commonly paid to it, namely, as a manoeuvrer to those 

 large ships in which engines of considerable power cannot be 

 placed, or in which it is considered unadvisable to place them. 

 No doubt can be entertained of the efficiency of such an instru- 

 ment worked by an engine of even fifty horse-power. The full 

 extent, however, of its utility cannot perhaps be thoroughly 

 appreciated until it shall have been extensively used in her 

 Majesty's navy." 



Since the date of this report that experience which was wanted 

 has been obtained, and the extensive use of the screw has been 

 adopted, and the results fully confirm all those anticipations. 



77. But it is not only in her Majesty's navy, but in the national 

 commercial marine, and not only as an auxiliary propeller, but as 

 an independent and most efficient agent of propulsion, that the 

 screw has been found to answer in practical navigation. In 1849, 



* Bourne "on the Screw-propeller," Chap. IV. 



165 



