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PLEASURES OF THE TELESCOPE.
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power of such an instrument divides the star into two twinkling points. They are about two and a quarter minutes of arc apart, and exceptionally sharp-sighted persons are able to see them divided
Map No. 17.
with the naked eye. Now take the three-inch telescope with a moderate power, and look at them. Each of the two stars revealed by the opera glass appears double, and a fifth star of the ninth magnitude is seen on one side of an imaginary line joining
