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Page:Popular Science Monthly Volume 32.djvu/275

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JOHN JACOB BAETER.

tudes of more than a hundred stations. Poggendorff paid him the compliment of discussing one of these determinations in "Annalen der Physic und Chemie," vol. ii, 1825, pp. 109-112.

In 1825 he was appointed a member of the faculty of the military school at Berlin, at first teaching pure and afterward applied mathematics; and from 1832 to 1857 he had charge of the department of geodesy, lecturing on the theory during the winter and working at it practically during the summer months. It was at the very beginning of his course in geodesy that Bessel secured his assistance in that monumental work, the degree-measurement in East Prussia, the results of which were published in 1838 under their joint authorship. While Bessel is known as the leading spirit in this undertaking, Baeyer's skill in handling instruments, his interest in base-measuring, and his efficiency in recognizance, contributed no little to its success. The accuracy, watchfulness, and painstaking detail of the enthusiastic officer stimulated Bessel to do his best; and this best so impressed itself upon Baeyer that posterity has become his debtor for having handed down and improved the methods of his honored master.

Before completing this work he received another call, this time through the intercession of Humboldt. The gravity experiments made by Bessel at the Berlin Observatory could not be of any especial value, owing to the uncertainty of the altitude of Berlin above sea level, which at that time was known only from barometric observations. Trigonometric leveling was now coming into great favor, especially when the precaution was taken to make reciprocal zenith-distance observations. So, when it was ordered by the general staff in 1835 that the altitude of Berlin above the mean sea-level at Swinemünde should be determined, the execution of the order fell upon Baeyer, who, with the assistance of Bartram, finished it during the same summer. The result obtained differs only by a few decimetres from that recently found by a line of geodesic levels. At Swinemünde a permanent mark was established, and annually for several years the height of this above mean tide was measured; these records many years later disproved the theory that the Baltic Sea had been subjected to a great change during the first half of this century in height.

He was placed in charge of the survey of the coast of the Baltic Sea in 1837, the triangulation for which he joined to that of the degree-measurement chain. This was carried up to annexation with the Danish work. In 1843 he was made chief of the trigonometric branch of the general staff, when he continued his great coast-survey, bringing the triangulation from Stettin to Berlin, and also connecting with Müffling's chain. These nets, together with Tranchot's and others, executed earlier for the purpose, formed the basis for the land survey of the Prussian states. Baeyer thought that work done at different times and by various persons should be brought into harmony by all resting upon the same basis; to which end he measured