To Show The Spots In The Sun's Disk By Its Image In The Camera
Obscura.
Put the object-glass of a ten or twelve feet telescope into the
scioptric ball, and turn it about till it be directly opposite the
sun. Then place the pasteboard mentioned in page 16, in the focus of
the lens, and you will see a clear bright image of the sun, about an
inch diameter, in which the spots on the sun's surface will be exactly
described.
As this image is too bright to be seen with pleasure by the naked eye,
you may view it through a lens whose focus is at six or eight inches
distance, which, while it prevents the light from being offensive,
will, by magnifying both the image and the spot, make them appear to
greater advantage.
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