Christian Henry Frederick, a German American astronomer, born at Colden-biittel, Schleswig, Sept. 19, 1813. After graduating at the university of Berlin he spent several years in travel and scientific explorations in Italy, Palestine, and the region of ancient Troy. He then came to the United States, was connected with the coast survey, and in 1858 was appointed professor of mathematics and astronomy in Hamilton college, and director of the observatory (now the Litchfield observatory), at Clinton, N. Y. In 1859, by exchange of star signals with the observatory of Harvard college, he determined accurately the longitude of his own observatory, and afterward of several other places in the state, and also of the observatory at Ann Arbor, Mich., which was made the fundamental point in the lake surveys of the United States. His last work of this character was the determination of the western boundary of the state of New York. Many of these labors were carried on under the auspices of the regents of the university of the state of New York. Dr. Peters took a prominent part at Des Moines, Iowa, in the observation of the total solar eclipse of Aug. 7, 1869. At his own observatory he has recorded in chronographic sheets over 20,000 solar spots, and has determined and catalogued, down to the 13th magnitude, 16,000 zodiacal stars.
He has also invented a polarizing eyepiece for solar work, by which the inconvenience arising from the great heat of large glasses is removed. Dr. Peters was chief of the party sent by the United States government to New Zealand to observe the transit of Venus of Dec. 9, 1874. He sent his assistant, Lieut. Bass, a month in advance to select a station. After careful examination a station in a mountainous region 130 m. inland was chosen as affording the greatest probability of a cloudless sky. The event justified their expectations. Dr. Peters's party was the only one on the island that was completely successful, and obtained 237 photographs of the transit. During the transit Dr. Peters by means of the double-image micrometer measured the apparent diameter of Venus, thus determining for the first time the real size of the planet, with an error of probably not more than 1/300 part of its value. M. Boquet de la Grye, chief of the French party, declared: "There is no need of other observations. Dr. Peters has accomplished all that was to be done." Dr. Peters is noted for his investigations in regard to comets and asteroids, having discovered 22 of the latter during the years 1861-'75, and determined their elements.
Wilhelm Karl Hartwig, a German naturalist, brother of the preceding, born at Ooldenbiittel, April 22, 1815. He studied in Copenhagen and Berlin, and became known by his exploration (1842 -'7), under the auspices of the Prussian government, of Mozambique, which he described in his Naturwissenachaftliche Reise nach Mossam-Mque (4 vols., Berlin, 1852-'68), from which Bleek compiled his " Languages of Mozambique " (London, 1856). He has been connected for many years with the medical department of the university of Berlin, and succeeded Lichtenstein in 1857 as professor of zoology and director of the zoological collections.