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First noticed to be variable in 1821 - by German Amateur Astronomer Johann Fritch.
"The German astronomers Argelander and Heis both began "regular" observing once every few years around 1842-1843, and the data from both men showed that the star became significantly fainter around 1847. Observers later in the 19th Century recorded another dimming event in 1874-1875, and another in 1901-1902."
The Earliest Light Curve of Epsilon Aurigae
Does this include all available data around the eclipse of 1901-02 or before, that is now known? Check
What were the spectroscopic observations made around this time? Check