Page:Popular Science Monthly Volume 57.djvu/20

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THE POPULAR SCIENCE MONTHLY.

gestions will be made. The instruments are divided into two classes, for visual and for photographic work. But in either case

PSM V57 D020 Relative images taken with different focal lengths.png
Chart V.— Relative Images of the Corona as taken with Telescopes ranging from Forty Feet to Four Feet in Focal Length.