for picking them out. The air is controlled by valves opened and closed by hand. Several methods are used to compress and exhaust the air. The most novel method consists in having tanks in which a partial vacuum is produced by allowing water to flow out of them into the sewer, or in having the air compressed by allowing water from the city mains to flow into the tanks and displace the air. Water jets have also been used, operating similar to a steam-injector. At some of the stations water turbines drive the air-pumps, and at others steam-engines are used. The tubes of the Paris system are of wrought iron, in lengths of from fifteen to twenty feet, the joints being made with flanges and bolts. The interior diameter is 2.559 inches with a maximum variation to 2.519 inches. The bends are made with a radius of from six to one hundred and fifty feet. Water frequently gives trouble by accumulating in the tubes. Traps are placed at low points to drain it off. The speed of the trains of carriers in the Paris tubes is from fifteen to twenty-three miles per hour, and the average time that elapses from the receipt of a message until its delivery is from forty to forty-five minutes. =The Pneumatic Telegraph of other Cities.=—A system similar to the one just described is used in Vienna. It differs some in details of apparatus, but the carriers are despatched around circuits in trains, stopping at each station, where some carriers are removed and others inserted. Brussels also is not without its system of pneumatic tubes for the transmission of telegrams. =Pneumatic Tubes in America.=—Turning our attention now to our own country, we cannot pass without mention some experiments of Alfred E. Beach with pneumatic railways, made nearly thirty years ago. His first experiment upon a large scale was made at the American Institute Fair held in New York City in 1867. Here he had constructed a circular wooden tube, one hundred and seven feet long and six feet in diameter. A car that would seat ten people ran upon a track laid down inside the tube, and was propelled by a helix fan ten feet in diameter, making two hundred revolutions per minute. He next tried his railway upon a practical scale, constructing an eight-foot tunnel for two hundred feet under Broadway, starting at the corner of Warren Street. A car was propelled by a large rotary blower located in the basement of a building near by. The blower was kept constantly running, and the car was sent alternately in one direction and then the other by changing valves at the blower. Few people know that this experimental line still exists under Broadway as Mr. Beach left it.