Show Curtains of Light Used to fo Measure Projectile Speed Ottawa Can An An artillery shell crashing through invisible invisible invisible ible curtains of light is the newest means of determining ing the speed of projectiles developed by scientists at the National Research Laboratories Laboratories Laboratories Labora Labora- tories here Particular merit of the system is its portability ity which enables it to be used in the field and bring added accuracy to computations computations computations of range in actual com com- bat Light Licht beams mirrors photoelectric cells and sensitive recording mechanism aro are the equipment which makes possible the Ute new new development development development de de- de- de of Dr D. D C. C Rose physicist physicist physicist cist In the division of physics and electrical engineering ut of the Canadian Canadian Canadian Cana Cana- dian Curtain of Light Used In effect the artillery shell passes down a narrow tunnel and every 50 feet teet intersects a beam of light falling fall taIl taIling falling ing on a photocell Momentarily the shell blocks off ol the light beam and this decrease in light intensity cuts C down the electrical output of ot the cell By an amplifying system this electrical change produces a permanent permanent permanent per per- manent record on photographic film turn In field tests at the military camp campat at Petawawa Dr Rose set up metal frames whose upper and lower surfaces surfaces surfaces sur sur- faces consisted of ot mirrors A beam of light started from the bottom and was reflected back and forth across the space between the mirrors until until un un- til Its ray finally fell feU on a photoelectric cell concealed In a small box attached to the upper part of ot the frame Thus the entire space within with with- in the frame was filled with a light beam which could b be blocked out by bythe bythe bythe the onrushing shell shellA A series serles of four tour of these frames were carefully lined up before an artillery piece which at a known and automatically registered instant In Instant instant in- in stant fired its shell through the frames |