THE OUTER PLANETS. 105 



really important discovery was made till 1878, 

 when Niesten at Brussels discovered the "great 

 red spot," a ruddy object 25,000 miles long by 

 7000 broad, attached to a white zone beneath 

 the southern equatorial belt. This remarkable 

 object has been observed ever since. In 1879 its 

 colour was brick-red and very conspicuous, but 

 it soon began to fade, and Bicco's observation 

 at Palermo in 1883 was thought to be the last. 

 After some months, however, it brightened up, 

 and, notwithstanding changes of form and colour, 

 it is still visible, a permanent feature of the 

 Jovian disc. In 1879 a group of " faculae," 

 similar to those on the Sun, was observed at 

 Moscow by Theodor Alexandrovitch JBredikhine 

 (1831-1904), and at Potsdam by Wilhelm Oswald 

 Lohse (born 1845). It was soon observed that 

 the rotation period, as determined from the great 

 red spot, was not constant, but continually in- 

 creasing. A white spot in the vicinity completed 

 its rotation in 5J minutes less, indicating the 

 differences of rotation on Jupiter. 



The great red spot has been observed since 

 its discovery by Denning at Bristol and George 

 Hough (born 1836) at Chicago. Twenty-eight 

 years of observation have not solved the mystery 

 of its nature. The researches made on it, in the 

 words of Miss Clerke, " afforded grounds only 



