100 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1934 



ling result that the period of rotation was found to be equal to the 

 period of revolution, the planet completing a rotation of 87*^.969256 

 round an axis almost perpendicular to the orbital plane. 



It is generally stated that Lowell did confirm the conclusions of 

 Schiaparelli. Yet in his 1896-97 map he does not show a single 

 marking observed at Milan, or elsewhere, but only an enormous 

 number of illusive blackish, linear canals, some perpendicular, others 

 parallel, others inclined to the plane of the orbit of the planet. 



On August 31, 1900, Barnard, using the 40-inch at Yerkes, de- 

 tected in broad daylight " 3 or 4 large darkish spots, very much 

 resembling those seen on the Moon with the naked eye," adding 

 that "one of these dark markings south preceding the center of 

 Mercury was specially noticeable." 



In 1907 and the years following, Jarry-Desloges and Fournier 

 drew some dusky spots of Schiaparelli's chart, which Sormano 

 believed to have been probably confirmatory of the long rotation 

 period. 



Five years later, Danjon, using a 7i/4-inch refractor in Paris, de- 

 picted admirably some real dark markings on the evening phase, 

 confirming Schiaparelli, and thus succeeding with a modest instru- 

 ment located in the smoke and dust of the great city there, where 

 Lowell had failed with a pow^erful telescope in the elevated and so 

 highly vaunted tablelands of Arizona. 



The conclusions of Schiaparelli met a cool reception. Yet a hand- 

 ful of astronomers, among them C. A. Young, E. W. Maunder, and 

 A. C. D. Crommelin, entertained but little doubt as to the accuracy 

 of the results of the Italian, while the majority of scientists opposed 

 to them a sturdy skepticism. It was thus only 4 years ago that 

 Graff wrote that almost nobody now believed in the 88-day rotation 

 period of Schiaparelli, controverted, as he thought, by the radio- 

 metric measures executed on the small disk of the planet. I never 

 accepted the deductions drawn from the interesting indications of 

 the thermocouple on the planets; and, in the case of Mercury at 

 least, my distrust was proved to be founded by the unexceptionable 

 evidence of observation. 



Prudence naturally prompted me to have no opinion on the rota- 

 tion period of that planet since I had not studied it telescopically ; 

 but, convinced that the powerful refractor of 33 inches aperture at 

 Meudon could easily help to solve the mystery, I asked my director, 

 M. Deslandres, for permission to use that instrument occasionally on 

 Mercury in daytime — a demand which was favorably received by that 

 most distinguished astronomer, and for which I wish to express here 

 my feelings of deep gratitude. 



