Der 40-Zoll-Refraktor des Yerkes-Observatoriums. Veröffentlichung der Meyers Enzyklopädie The 40-inch refractor of the Yerkes Observatory. Publication of the Meyers encyclopedia, Vol. 7, Leipzig, Germany, 1910. LicenseRF Copyright: xZoonar.com/SergeyxKohlx 23189392

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