48 ANNUAL OF SCIENTIFIC DISCOVERY. 



been made successful in England. The vessel in question is of iron, 

 four hundred tons, and one hundred and sixty feet in length, having 

 two independent engines and screws, with a collective nominal horse- 

 power engine of one hundred and twenty horses, the screws working 

 under each quarter, and consequently before the rudder, in lieu of 

 the present system of one screw astern and abaft the rudder. The 

 use of two screws in the propulsion of ships is nothing new ; but this, 

 it is stated, is the first instance in which a vessel has been fitted with 

 two screws and engines working separately and independently of 

 each other ; and herein lies the value of the principle in a military 

 point of view, as giving a ship a means of rapidly revolving under 

 steam, and changing her position to any required point. In the trial 

 trip, the following experiments were made with a view of testing the 

 capability of the ship for rapid turning within a small space. The 

 first was made with both engines, going ahead at full speed, and the 

 helm hard over, when the first circle was made in three minutes and 

 fourteen seconds, the second in three minutes and thirteen seconds, 

 and the third in three minutes and sixteen seconds, the diameter of 

 the circles being about three lengths of the ship, and lessening each 

 time. In the second experiment, one engine and screw worked 

 ahead, with the other going astern, and one circle was made in three 

 minutes and thirty-nine seconds, and another in three minutes and 

 forty-nine seconds. In making these circles, the action of the ship's 

 hull was extraordinary, the central part being stationary, and both 

 ends moving round equally ; the circle was made on a pivot from the 

 ship's midship section. The vessel was then put in a straight course, 

 stopped, and from a state of rest the engines were started, one ahead 

 and the other astern, the circle being completed in three minutes and 

 fifty-five seconds, and the diameter of the circle being, as before, 

 within the ship's length. 



UNSINKABLE AND INCOMBUSTIBLE SHIPS. 







During the past year there has been constructed and launched in 

 England a screw-steamer, which is claimed by the builder, Mr. C. 

 Lungley, to have two great and novel advantages, viz., safety from 

 destruction by water, and, to a great extent, security against fire. 

 Each deck of the vessel is distinct from the others, having no commu- 

 nication with them, but having its separate hatchway or entrance 

 from the upper deck ; the object of this arrangement being, that 

 whatever injury may be incurred by either one, or even by two, of 

 these decks or stories, the other or others will float. Thus, for 

 instance, should the lower or keel deck be knocked away, the two 

 upper decks will float the ship ; or should, either from a collision, the 

 starting of a plate under the water-line, or from a shot or a broadside 

 penetrating tlifi sheathing, one of the intermediate decks let in the 

 water, even to the extent of filling the compartment from stem to 

 stern, the buoyant power would still remain, and the vessel would 

 not only float, but be perfectly manageable, the water merely rising 

 up the trunk hatchway of that particular deck to the level of the 

 water-line outside, allowing full opportunity for a diver to descend, 

 find out the place and extent of the injury, and repair it if capable 



