102 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 19 34 



My results are embodied in the figure accompanying this paper. 

 A closer scrutiny with the large telescope, and with better definition 

 under a high Sun, would have revealed a much more detailed struc- 

 ture; but the present map gives a satisfactory view of the most 

 important markings seen by me with certainty on that desolate world. 



The color of Mercury looked at daytime in the 33-inch almost com- 

 parable with that of the Moon in twilight. The planet appeared 

 yellowish with a slight roseate tinge on the azure of the sky ; while 

 a distinct neutral-gray hue was characteristic of its dusky areas.' 



With the view of avoiding the use of periphrases in the description 

 of the spots, I have given names to the latter, generally drawn from 

 the Greco-Egyptian mythology of the god Mercury. A few names 

 were inspired by the desert state and tremendous heat prevailing on 

 the planet; and I deemed it a duty to christen a bright area by the 

 name of the antique Liguria^ in pious remembrance of Schiaparelli, 

 born at Savigliano, for his truly wonderful discovery of the chief 

 spots and slow rotation of Mercury with a small telescope. 



The dusky markings of the planet appear larger in the 33-inch 

 than in the telescopes of the Italian astronomer — a fact due to dimin- 

 ished diffraction in the big glass, and one, too, which yields a precious 

 independent proof of the reality of the markings in question. 



The largest of the gray spots was named " Solitudo Hermse Tris- 

 megisti ", or " Wilderness of Mercury the Thrice Greatest " — a fabu- 

 lous personage, believed by the Greeks and the Egyptians to have 

 invented all sciences, including astronomy. This marking was dis- 

 covered, among others, by me at Meudon; it had not been seen 

 previously on account of its faintness, and I have shown that 

 medium-sized instruments do not reveal pale half-tones on the 

 planets.* 



The dark area named Solitiido Atlantis, to the right of my map, 

 is certainly much larger now than when it was first drawn 53 years 

 ago. Yet the reality of this apparent change must be considered 

 with the utmost diffidence, as vegetation seems impossible on a world 

 where the temperature rises at least 200- above the zero of the 

 Centigrade scale. 



rests on no decisive spots, but on an effect of contrast. The faint markings seen by 

 me on Venus were manifestly atmospheric and variable from 1 day to the other. A 

 calculation of the solar tides on Venus has shown me that her rotation was slackened 

 only twice as much as that of the Earth. Should the absence of a satellite constitute 

 an Indication of a slow original rotation (which is doubtful), then the neighbor planet 

 may have a rotation period extending over months, which seems to agree with my 

 observations. In fact, definite spots appeared fixed here several times during more than 

 3 hours. 



* Schiaparelli found that these spots had a pale brown tinge. This I could not confirm, 

 in spite of the great superiority of the large instrument in showing color. Mars, Jupiter, 

 and Saturn display wonderful hues in it ; but the dark spots of Mercury always appeared 

 to me quite as colorless as the Maria of the Moon. 



*■ Mars Report for 1909, in Mem. British Astron. Assoc, vol. 20, p. 30. 



