The present surface condenser consists essentially of a great number of small brass tubes, about three-fourths of an inch in diameter, passing through an air-tight chamber. The exhaust steam from the cylinders enters the chambers, and cold water is constantly pumped through the tubes. The steam is condensed by contact with the cold tubes, and the water thus obtained pumped back to the boiler in a fresh state, instead of being mixed with about thirty times its weight of salt water, as in the old jet condenser. Practice varies, the steam sometimes being passed through the tubes and the water around them. The late Dr. Froude investigated this matter some years ago, and showed that such results were quite possible, independently of any fining of the lines, owing to the effect on the ship of the waves set up when in motion. One very curious illustration of how such waves may seriously affect a vessel is in that of a yacht built many years ago by an eminent firm on the Clyde, which failed to come anywhere near the performances guaranteed owing to the fact that as the speed increased the hollow following the wave formed at the bow increased and approached nearer and nearer to the paddle-wheels, until the water dropped below the floats and allowed the wheels to spin in the air; the propelling effect was thus entirely lost until the vessel slowed down sufficiently for the water to rise again to the level of the paddle-wheels. Such a thing could scarcely happen with a screw steamer; but the very bad steering qualities of certain naval ships is due to the fact that the inrush of water at the stern causes currents to flow with the ship, and therefore to produce quite different results with the rudder from those which generally obtain. There is one line of steamships from New York direct to Indian, Chinese, and Japanese ports by way of the Mediterranean Sea and the Suez Canal. It is operated by Edward Perry & Co., and case oil forms the bulk of the trade. About one vessel a month is sent out, and this vessel has a tonnage of about 3,000 gross. Carter, Hawley & Co., and Carter, Macy & Co., had during the year 1891 about 25 steamships consigned to them from China and Japan, the tonnage of which was about 60,000 gross. Inward these vessels are tea-laden, but on the return trip they are usually chartered by other firms for general cargo. |