In the Woolworth Building, New York, the highest elevator shafts are 680 feet high and the air pockets are 137 feet deep--i. e., they reach up to the tenth story. If the car broke away from its supports at the top of the shaft it would be traveling at the rate of 132 miles an hour when it struck the air pocket, but before it reached the bottom the air would bring it practically to a stop. Imagine a heavy automobile traveling at 132 miles per hour and brought down to a standstill in half a city block! The passengers would be hurled out of their seats, but in an elevator the passengers are standing and can brace themselves against the pressure produced by their own momentum. The velocity acquired in falling 543 feet to the air pocket must be overcome in 137 feet or ¼ of the distance. This means that the weight of each passenger is multiplied by four. A man who weighed 150 pounds would find that his pressure on the floor of the car had mounted to 600 pounds. One of the inventors of the pneumatic cushion for elevators was killed when testing out a car, not because of the impact of the car, but because he was foolish enough to sit in a chair. The chair gave way under his suddenly acquired weight and the poor man was fatally stabbed by one of the splinters. Air jets are used for a variety of purposes ranging from tamping railway tracks to painting buildings. When a track is depressed under the tamping action of trains passing over it the ties must be raised and new ballast introduced under them so as to bring them up to level. In order to save hand labor and insure the perfect filling of all cavities a pneumatic tamper is sometimes used. The ballast, consisting of sand or gravel up to ¾ inch in diameter, is fed out of a hopper and meets a blast of air that hurls it into place like shot from an air rifle. This furnishes a very solid and compact road bed. It is in much the same way that weather-stained stone walls are cleansed by means of a sand blast. The sand particles projected by the jet of air act like myriads of tiny bullets which chip away the face of the stone. LAYING CEMENT WITH AN AIRGUN It is after this same fashion that the cement gun is used to project cement against wire reenforcement to form walls of buildings. Carl E. Akeley was led to the invention of the cement gun by his efforts to find an expeditious and economical method of mounting specimens of large animals for the Field Museum in Chicago. He constructed a pneumatic device for spraying cement and water upon a canvas-covered framework, thus building up a body upon which the skin of the animal could be mounted. This machine was improved and tried out successfully, on a large scale, in constructing buildings.