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Work on the Coolidge dam across the Gila river not far from Phoenix, Ariz., is rapidly nearing completion and engineers are studying it with special interest because of its form of construction. It is of what is known as the multiple-dome type and is said to be the largest of this kind in the world. The buttresslike form is intended to give greater strength. The dam has been built by the United States reclamation service and the Indian department at a cost of approximately $3,500,000.

 

Projection of television images on a large screen, in the same manner in which movies are shown, is planned by C. Francis Jenkins, televisor and radio-movie inventor. If the method on which he is working succeeds, the chief problem of television reception—the smallness of the image possible with all existing systems—will be solved. In the old Jenkins process, as in all others, a scanner is used to reproduce the picture. The Jenkins scanner had forty-eight holes, drawing forty-eight successive lines of light, and, as the picture is square, the effect is of forty-eight times forty-eight dots, or a total of 2,304 separate units. Behind the scanner disk is a neon light, the intensity of which is controlled by the received signal, and the illusion of a picture depends on the persistence of vision in the eye, the light of each line lingering until all of them have painted a complete picture. In his new system Jenkins is using 2,304 small incandescent flashlight lamps, mounted closely together in a square bank. A revolving switch or commutator connects the lamps successively to the radio set to receive the incoming signals. But, unlike the neon light, the filament of the incandescent lamps continues to glow for an instant after the current is turned off.

