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222 supplied by Captains King and Fitz Roy, and are taken from a little work by Sabine, (Magnetic Observations made during the Voyages of H. B. M.'s Ships Adventure and Beagle, 1826–1836.)

The determinations for the several other stations are taken partly from the above-named sources, and partly from the following:

1. Spitzbergen. Observer, Sabine, 1823. (From his Account of Experiments to determine the Figure of the Earth.)

2. Hammerfest. The declination and inclination are the means of the determinations of Sabine, 1823 (Pendulum Experiments); and of Parry, 1827. (Narrative of an Attempt to reach the North Pole.)

3. Magnetic Pole, from Captain James Ross, 1831. (Phil. Trans. 1834.)

4. Reikiavik, from observations by Lottin, 1836, (Voyage en Islande.)

28. Berlin, from Encke, 1836. (Astronomisches Jahrbuch, 1839.)

38. Göttingen. The declination is for October 1, 1835 (Resultate für 1836, page 39); the inclination is reduced to the same epoch by interpolation between von Humboldt's observation in 1826, and Forbes' in 1837.

39. London, from observations communicated in manuscript. The declination, by Captain James Ross, for the mean epoch, April, 1838; and the inclination by Phillips, Fox, Ross, Johnson, and Sabine, for the mean epoch of May, 1838.

48. Paris, for 1835, from the Annuaire for 1836.

54. Milan, 1837, by Kreil. Communicated by him in manuscript.

58. Naples, from observations by Sartorius and Listing. The intensity, which was determined according to absolute measure, has been reduced to the common unity, by the application of the factor given in Article 31.

64. Madras, 1837, from observations by Taylor, taken from the Journal of the Asiatic Society of Bengal, May, 1837.

In judging of the differences between calculation and observation, as shown in the foregoing tabular comparison, it must be remembered, on the one hand, that almost all the observations are charged both with the errors of observation, and with the