50. Four views of Mars, showing canals. (Lowell)

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49. Two views, showing seasonal change on Mars. (Lowell)

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48. Three photographs of Mars, showing rotation. (Yerkes Obs.)

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47. Drawing of Mars. (Trumpler, Lick Obs.)

46. Diagram of motions of earth and Mars, 1926.

45. Photograph of crescent Venus. (Barnard, Yerkes Obs.)

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44. Motion of Venus as seen from earth. (Copyright)

43. Mercury, the swift messenger of the gods.

42. Key to photograph, No. 41.

41. Portion of moon. (Mt. Wilson Obs.)

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