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Show ROTATING DISK APPEARS TO BE HOLDING STILL That by proper illumination a rapidly-whirling disk can be made to appearto be stationary is demonstrated dem-onstrated by apparatus on display dis-play in the physics store-room in the science building at Dixie junior jun-ior college. It consists of two motor-driven cardboard disks, one provided with a slit and the other with letters. A beam of light is directed di-rected through the slitted disk and ifalls onto the center of the lettered disk. When the two are rotating at exactly - the same speed, the letters on the latter appear stationary. If one is whirling whir-ling slightly faster than the other, the letters seem to be moving slowly in one direction or the other. This phenomenon is known as stroboscopic illumination, according accord-ing to M. J. Miles, head of the physical science department at the colege. It is essentially the same principle as is used in moving mov-ing pictures, where to the observer obser-ver the images do not appear to be sliding down the screen, as they should if the shutter should fail to work. The slit in the disk acts the same as a shutter, allowing allow-ing light to fall on any one point , on the ether difk when it is in but one position. This is the latest of a series of demonstrations by the chemistry and physics department at the college. |