Ivory's treatment of pendulum observations

James Ivory (1765–1842) contributed to the mathematical theory of attraction. I describe his efforts (1826–1830) at determining the earth's ellipticity (e) through the adjustment of pendulum observations. At the time, several dozens of such observations had already been made in various latitudes, and their adjustment presented difficulties owing to the local anomalies of gravity. The very possibility of deducing a single ellipticity for the earth remained questionable. While achieving his goal, Ivory made methodical mistakes which he gradually corrected. His final result, 0.00333 < e < 0.00338, compares favorably with the value e = 0.00335 of the so-called Krasovsky ellipsoid. Ivory's work was forgotten mainly because new data, especially on meridian arc measurements, became available rather soon after its publication