Translations:Adventist Youth Honors Answer Book/Health and Science/Optics/59/en
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9. Construct one optical instrument using mirrors or lenses, such as a periscope, a slide or opaque projector, or a simple telescope.
Periscope
A periscope is an instrument for observation from a concealed position. In its simplest form it is a tube in each end of which are mirrors set parallel to each other and at an angle of 45° with a line between them.