THE INNER PLANETS. 85 



but as Herschel was unable to observe the mark- 

 ings seen by Schroter, many astronomers were 

 inclined to be sceptical regarding the accuracy 

 of the Lilienthal observer's results. Schroter 

 also observed the southern horn of Venus when 

 in the crescent form to be blunted, and he 

 ascribed this to the existence of a great 

 mountain, five or six times the elevation of 

 Chimborazo ; while he observed irregularities 

 along the terminator, which he considered to be 

 more strongly marked than those on the Moon. 

 Schroter's opinion on this point, although re- 

 jected by Herschel, was confirmed by Madler, 

 Zenger, Ertborn, Denning, and by the Italian 

 astronomer Francesco Di Vico (1805-1848), 

 director of the Observatory of the Collegio 

 Romano. In 1839 Di Vico attacked the 

 problem of the rotation, and his results were 

 confirmatory of those of Schroter. He estimated 

 that the axis of Venus was inclined at an angle 

 of 53 to the plane of its orbit. Meanwhile 

 a series of important observations had been 

 made on Venus by the Scottish astronomer 

 and theologian, Thomas Dick (1772-1857), who 

 suggested daylight observations on Venus to 

 solve the problem of the rotation. 



In 1877 the question was attacked by 

 Schiaparelli, who commenced a series of ob- 



