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l appear fully equal to that of circles of the larger dimension. The comparison with the two stations, at which a more than usual attention was bestowed, is the more appropriate, because it was essential to the purposes for which the latitudes of the French stations were required, that the observations should always be conducted with the utmost possible regard to accuracy. "It would appear, therefore, that in a repeating circle of six inches, the disadvantages of a smaller image enabling a less precise contact or bisection, and of an arch of less radius admitting of a less minute subdivision, may be compensated by the principle of repetition." Captain Sabine has pointed out Maranham and Spitzbergen as places most favourable to the comparison. Let us take the former of these places, and compare the observations made there with the small repeating instrument of six inches diameter, with those made by the French astronomers at Formentera, with a repeating circle of forty-one centi-metres, or about sixteen inches in diameter, made by Fortin. It is singular that this instrument was directed, by the French Board of Longitude, to be made expressly for this survey, and the French astronomers paid particular attention to it, from the circumstance of some doubts having been entertained respecting the value of the principle of repetition. The following series of observations were made with the two instruments. [I have chosen the inferior meridian altitude of Polaris, merely because the number of sets of observations are rather fewer. The difference between the extremes of the altitude of Polaris, deduced from sets taken above the pole by the same observers, amounts to seven seconds and a half.] Latitude deduced from Polaris, with a repeating circle, 16 inches diameter.--BASE DU SYSTEME METRIQUE, tom. iv. p. 376. 1807. Number of Latitude Names of Observers. Observations. of Formentera. deg. min. sec. 64 38 39 55.3 Biot 100 54.7 Arago 10 56.2 Biot 88 56.9 Biot 120 56.7 Arago 84 54.9 Biot 100 56.5 Arago 102 57.1 Arago 80 54.5
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