Lowell, Percival, 1855-1916 · New York, The Macmillan Company · leaf 261
doing the latter disclosed a very interestingfact. It was evident that the markings held in generala definite fixed position upon the illuminated part ofthe disk, showing that the planet kept the same facealways to the Sun. But systematic observation, con- 222 THE EVOLUTION OF WORLDS tinued day… … Diagram of libration in longitude due to rotation. singular systematic sway stood revealed the librationin longitude caused by the eccentricity of the planetsorbit. Mercury revolves about the Sun in an ellipse moreeccentric than that of any other principal planet. Attimes he is half as far off…
Cosmogony
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