Struves career at Dorpat geodesy double stars and the search for parallax

In 1815, shortly after Napoleon's final defeat at Waterloo, Struve married Emilie Wall in Altona and brought her to Dorpat. Little is known about Emilie's personality or her perspective on her new life with Struve, but her experiences were at least physically taxing. In 19 years, she carried 12 babies to term, beginning with Gustav, born in 1816, Alfred, born in 1817, and Otto, born in 1819.

Struve tried to reserve Sundays for family gatherings, but nights at the telescope and work-related travel often kept him away from home. He embarked on two main research projects that would dominate his 25-year tenure as a professor at Dorpat. The first of these, which he worked on mainly during the summers, was a series of land surveys on a scale large enough to take into account the Earth's curvature. The second—well suited to take advantage of long winter nights — was his study of double stars and stellar parallaxes, leading to his magnum opus on stellar astronomy and the distribution of stars in the galaxy, the Etudes d'Astronomie Stellaire [Studies in Stellar Astronomy].

In 1815, an organization called the Livland Public Utility and Economic Society asked Struve to survey the Russian province of Livland, territory that comprises the modern nations of Estonia and Latvia. It was an important project, as the survey formed the basis of new maps showing the precise location of hundreds of landmarks, and included information on elevation above the Baltic sea level, essential for planning public works in this area of extensive wetlands and swamp forests.

Upon completing the Livland survey in 1819, Struve proposed to the Russian Czar Alexander I, through university intermediaries, an even more substantial geodetic survey. He would measure the length of an arc of longitude stretching from an island in the Gulf of Finland to a town in present-day Latvia, considerably longer than the span available from the Livland survey. The project was approved, and this work kept Struve busy until about 1851, as he linked the initial survey to others in progress and, after 1825, petitioned the new Czar Nicholas I for funds to extend that work also. He finally came to supervise a multinational effort to measure an arc from the shores of the Barents Sea in extreme northern Norway to the city of Izmail (Ukraine) near the Black Sea. This arc, covering a distance of some 1800 miles (3000 km), is sometimes known today as the Struve Arc.

Struve's involvement in geodetic surveys followed naturally, if not inevitably, from his technical expertise, his passion for pursuing fundamental questions in science, and his position in Russia's most westernized university. All western powers carried out large-scale surveys in the nineteenth century, the better to assess the extent of their territories or overseas empires and to plan for their commercial exploitation. The British embarked on a trigonometric survey of India in 1802; the Americans established the precursor to their Coast and Geodetic Survey agency in 1807, beginning work on their transcontinental arc in 1871; Bessel himself carried out a triangulation of East Prussia in the 1830s; the Dutch mapped Indonesia in the 1860s; the French produced topographic maps of Southeast Asia in the 1880s. Struve's surveys helped link the westernmost provinces of the Russian empire to their European neighbors, physically and politically.

The geodesist's instruments for measuring positions and angles are essentially the same as the astronomer's, so governments usually tapped observatory directors for national surveys. For Bessel and Struve, the surveys also carried the allure of big questions in science. In the late 1600s and early 1700s, a set of French surveys showed a curious thing: the length of a degree of longitude measured north of Paris appeared to be shorter than a degree south of Paris, suggesting that the Earth is slightly egg-shaped. If the Earth were perfectly round, a degree of longitude would be the same length everywhere; if, as Isaac Newton had convincingly argued, the Earth were rather flattened at the poles, a degree should be slightly longer north of Paris, not shorter. Indeed, Newton's explanation of precession depended on the Earth's having an equatorial bulge and polar flattening.

British scientists vehemently dismissed the French data suggesting an egg-shaped Earth. To settle the question, the French Academy of Sciences dispatched geodesists to the equatorial regions of South America and to Lapland, to measure the lengths of arcs in these two extreme positions. The results of these eighteenth-century expeditions clearly vindicated Newton's theory, and stimulated more interest in the exact shape or ''figure'' of the Earth.

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