Word: shutter
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Dates: during 1900-1909
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...prism is placed, which breaks up the light of the stars so that by the study of the rays the composition and character of any one star may be accurately determined. The second instrument is regulated by two ordinary alarm clocks, which open and close the shutter at any time the operator may wish. Every night this telescope is pointed directly at the north star, and after an exposure of twelve hours a semi-circle is thus traced on the plate. By this device an impression on the plate is made both of clouds and stars and a record...