32 ANNUAL OF SCIENTIFIC DISCOVERY. 



entire action very closely approximates to that of a screw applied to 

 surface propulsion. The invention is highly recommended by compe- 

 tent authorities, the increased velocity derivable from its use being esti- 

 mated at from one sixth to one eighth. London Mining Journal. 



IMPROVEMENTS IN THE CONSTRUCTION OF SHIPS AND STEAMERS. 



THE following extract from the last report of the Secretary of the 

 Navy furnishes a striking illustration of the rapid advances recently 

 made in this country in the construction of ships and steam-vessels : 



" In everything pertaining to the building, armament and equip- 

 ment of vessels of war, the scrutinizing and active mind of the present 

 age has not been idle. Merchant vessels of large draught have recently 

 been built and rigged in our country, which have sailed, by the force 

 of the winds alone, one thousand statute miles in three days, and with 

 an approach to the like rate of speed in long voyages. Improvements 

 and discoveries in ordnance and gunnery have been introduced, by 

 means of which, in the opinion of well-informed officers, a ship of infe- 

 rior rating say of 32 guns may be so built and rigged and armed 

 as to prove more than a match for the stoutest line-of-battle-ship of 

 the old construction and armament. How far the power of steam may 

 be added to increase the superiority of the modern vessel in speed, 

 destructiveness, and other points of a man-of-war, is also a fruitful 

 theme of speculation and experiment. In illustration of one of the 

 improvements in war steamers, it is represented to the department that 

 the boilers of the Mississippi, planned fifteen years since, and with tho 

 best intelligence of the day, may be reduced nearly one half in their 

 dimensions and weight ; and, at the same time, made to double the 

 power of the vessel, with about the same expenditure of fuel as at 

 present." 



SCREW vs. PADDLE 



AN interesting experiment took place recently, at Copenhagen, 

 between two steam-vessels of equal size, 800 tons and 260 horse-power. 

 Each vessel's engines were made by Maudsley, of London. The Hol- 

 gerdenser (paddle), carrying two 60 pounders and six 24's, and the 

 Thor (screw), carrying fourteen 32's, were lashed stern to stern, when 

 the Thor towed the paddle at the rate of 2f ths knots per hour 

 through the water, in spite of her full power applied to her paddles. 

 Boing disconnected, they were then tried against a strong breeze, 

 when the screw again had the advantage over the paddle ; but when 

 they were put before the wind (no sails set) the paddle had the advan- 

 tage of the screw to the same extent. Both vessels were of similar 

 model, the paddle being a little longer, narrower, and sharper than 

 the other. Both had their armaments, as above, and a full comple- 

 ment of coals on board ; the paddle drawing 12 feet 3 inches aft, and 

 12 feet forward ; the screw, 15 feet 6 inches aft, and 14 feet forward. 



