Page:Popular Science Monthly Volume 91.djvu/29

 Not Always Believe Our Own Eyes and Ears

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� ��Another trick played on the eye is shown in the illustra- tion at the left. A man looks through a lens at an object placed a short distance from it. The object is then moved farther away and the lens is removed. The brain realizes that the distance has been increased and here again the iris of the eye widens, even though the intensity of light was not altered

���Acuteness of hearing is determined by varying the volume of sound let into the ear through an opening in a tube. For some people the full volume of sound may be audible through a tiny section of the opening while others get it only through the fully opened tube

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��Your sensitiveness to tempera- ture may be tested by placing your hands in two jars of water of different temperature. If the hands are crossed as in the picture above, it will be almost impossible to tell by the sense of feeling which hand is in the hot water and which in cold

��Photos by Jacques Boyer

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