MARKINGS OF MERCURY ANTONIADI 



101 



The planet was thus followed near the meridian during the summer 

 months of 1927, 1928, and 1929; and it was soon obvious that its 

 markings, which were often seen quite distinctly, appeared fixed with 

 regard to the terminator for hours together on the same day. Yet 

 they showed, day after day, a pronounced movement of libration in 



FiGURH 1. — Chart of Mercury. Embodying all the markings observed on the planet 

 with the 33-inch Refractor at Meudon, in 1927, 1928, and 1929. By E. M. Antoniadi. 



The central point. Z, is supposed to have the Sun at the zenith when the planet is in 

 perihelion or aphelion ; but as the projection is not an orthographic one, the chart does 

 not give the approximate appearance of Mercury in superior conjunction with the Sun. 



The letter S. stands for the initial of the Latin word Solitudo, wilderness.; and the 

 abbreviation Prom, stands for promontonuw. 



Argyritts is a bright white region, and was discovered in 1882 by the English astron- 

 omer, W. F. Denning. 



longitude, such as would be necessitated by a uniform rotation of 

 Mercury in a period equal to that of the revolution round the Sun, 

 The axis was found almost perpendicular to the plane of the orbit, 

 its inclination not reaching 7°. Here, then, we had a complete 

 vindication of the conclusions of Schiaparelli.^ 



' I must state that a very close scrutiny of Venus near the meridian for many months 

 in 1928 with the large telescope has convinced me that Schiaparelli's period of 225'' 



