ENGLAND’S SECOND LARGEST AIRSHIP READY TO TAKE FLIGHT

With the completion of the rigid airship, R-100, England now has the two largest airships in the world. Like the R-101, which has been in the air for about two months, the new ship has a capacity of 5,000,000 cubic feet, as compared with the 2,600,000 cubic feet of the Los Angeles and the 3,708,000 cubic feet of the Graf Zeppelin.

ELECTRIC EYE

Constantly measuring the smoke and haze in the Holland Tunnel under the Hudson River connecting New York and Jersey City is the latest job for science’s magic lamp, the photoelectric cell, that has made television and talking movies practicable.

Above the main tube of the tunnel, through which traffic passes, is an exhaust duct, a long, cave-like chamber near the New York end. Through this duct is drawn the exhaust air from the tunnel. The duct is at the point where the roadway grade is greatest and where there are the most exhaust gases from the heavy truck traffic. Except for the light admitted through the air openings, the duct is dark.

Here General Electric engineers have installed experimentally a photoelectric device to measure the smoke and haze. A large box contains a lamp and a photoelectric cell in adjacent compartments, light-tight except for a lens at the front of each. The lens in front of the light makes a narrow beam, which shines on a mirror 150 feet away. Thence it is reflected to a second mirror and back to the box, where the other lens focuses the light on the cell. The current from the cell is amplified by vacuum tubes, and passes over wires to the recording device in the tunnel office a half mile away. Here it controls the movement of a pencil over a moving strip of paper.

When the amount of smoke in the air duct increases, the intensity of the light returning to the photoelectric cell is reduced, and the moving pencil immediately indicates the fact. Then the tunnel engineers can turn on more of the ventilating fans to keep the air clear.

Uses for such a device in homes and business offices are foreseen, where it can be used to detect smoke and act as a fire alarm. For some time the Holland Tunnel has used a somewhat similar device to count traffic, by the interruptions by automobiles of a beam of light across the exit.