86 A CENTURY'S PROGRESS IN ASTRONOMY. 



servations on Venus at Milan in that year. 

 The results of his studies were summed up in 

 1890 in five papers contributed to the Milan 

 Academy. He came to the conclusion that the 

 markings observed by Schroter, Di Yico, and 

 others were not really permanent, and concen- 

 trated his attention on round white spots, which 

 remained fixed in position. Instead of observing 

 Venus in the evening, Schiaparelli followed it by 

 day, watching it continuously on one occasion 

 for eight hours. But the markings remained 

 fixed. Schiaparelli accordingly concluded that 

 the planet's rotation was performed in prob- 

 ably 225 days, equal to the time of revol- 

 ution. One face is turned towards the Sun 

 continually, while the other is perpetually in 

 darkness. 



The announcement was so startling that, as 

 Miss Clerke says, " a clamour of contradiction 

 was immediately raised, and a large amount of 

 evidence on both sides of the question has since 

 been collected." Perrotin at Nice, Tacchini at 

 Rome, Cerulli at Teramo, Mascari at Catania 

 and Mount Etna, and Lowell in Arizona, all 

 in favourable climates, confirmed Schiaparelli's 

 results, as also did a second series of observa- 

 tions by the Milan astronomer himself in 1895. 

 On the other hand, Neisten, Trouvelot, Camille 



