20 ANNUAL OP SCIENTIFIC DISCOVERY. 



scientifically fitted, might be overrun by an adversary, and come up 

 on the other side. He claimed the introduction into the navy of the 

 air-tight compartments, by constructing a vessel upon the plan of a 

 ship within a ship the outer, sectional compartments each independ- 

 ent per se for coals or stores ; the inner to contain compartments and 

 accommodation, if necessity demanded, for the crew. The oval form 

 would secure the means of withstanding, externally, any compression ; 

 it would facilitate the delivery of coals from the bunkers, and if any 

 one of those bunkers was perforated or stove, you possessed the en- 

 gine-power, to be exerted from within, of expelling the water, by 

 ibrcing- in air, making every such valve self-acting from the interior. 



STEERING SCBEW FOR STEAMERS. 



Some experiments have recently been made by the British Admiralty 

 on a new arrangement of that screw propeller which has for its object 

 steering, as well as the propulsion of a vessel. ' The peculiarity of the 

 screw is that a universal joint is placed within the hollow boss of the 

 screw, which is thereby connected with the main shaft, the centre of 

 gravity of the screw and the centre line of the rudder intersecting 

 the centre line of the main shaft, so that the entire weight of the 

 screw is borne by the shaft ; and by means of a tail or spindle to the 

 screw, projecting from the boss working in the rudder, or an iron car- 

 rier in lieu of rudder, whatever may be the movement of the tiller or 

 wheel, it communicates an equal movement to the screw, which be- 

 comes not only the propelling but also the guiding power of the ship. One 

 of these screws, fitted to a naval steamer of sixty-horse power, has been 

 tried upon the Thames, and the result is reported in the London Post, 

 as unequivocally satisfactory, "clearly demonstrating that it is no 

 longer needful to apply double screws, hydraulic steering apparatus, 

 or add any other extra complications to the machinery of a steamer, 

 when by a wave of her own screw, her motion can be directed and con- 

 trolled at will." 



RAILWAY TUNNELS IN GREAT BRITAIN. 



At a recent meeting of the Institution of Civil Engineers, Mr. J. S. 

 Eraser stated that the aggregate length of the tunnels, now daily 

 traversed by railway trains in the united kingdom, amounts to eighty 

 miles ; and, supposing their cost to have been on an average fifteen 

 pounds per lineal yard, their construction must have caused the ex- 

 penditure of six and a half millions sterling. 



STEEP RAILWAY INCLINE. 



The Bhore Ghaut Incline of the Great Peninsular Railway of India 

 has occupied more than seven years in construction, and during the great- 

 er part of that time there have been 45,000 workmen daily employed 

 upon it. The incline is a series of tunnels through mountains of 

 rock, and viaducts stretching across valleys, alternating with each 

 other; each part a triumph of modern science and skill. 



The incline reaches at one long lift the height of 1,832 feet, the 

 highest elevation yet attained by any railway incline. It is lo^ miles 

 long, and its average gradient consequently 1 in 4G.39. The highest 

 gradient is one in 37, and the sharpest curve 15 chains radius. The 



