M51 as drawn by Lord Rosse, 1845
The illustration above is a drawing of the Whirlpool Galaxy made in 1845 by William Parsons, the Third Earl of Rosse. Lord Rosse’s 72-inch telescope enabled him to see the spiral shape of the Whirlpool. Like many astronomers, he drew the bright parts of the image with a dark pencil, making his drawing look like a photographic negative.
More information can be found in the Telescopes From the Ground Up activity.http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/basics/g44/