CORRECTIONS AND ADDITIONS. 



PAGE 85. LINE 9. 



Though the nearness of the moon in comparison with the sun does 

 not seem to compensate the smallness of her mass, yet the already well 

 ascertained alteration of the magnetic declination in the course of a 

 lunar day, the lunar-diurnal magnetic variation (Sabine, in the Report 

 to the Brit. Assoc. at Liverpool, 1854, p. 11, and for Hobart-town in the 

 Phil. Tr. for 1857, Art. i, p. 6), stimulates to a persevering observation 

 of the magnetic influence of the earth's satellite. Kreil has the great 

 merit of having pursued this occupation with great care, from 1839 

 to 1852, (see his treatise Ueber den Einfluss des Mondes auf die hori- 

 zontale Component der Magnetischen Erdlcraft, in the Deukschriften der 

 Wiener AJcademie der Wiss. Mathem. Naturwiss. Classe, vol. v, 1853, 

 p. 45, and Phil. Trans, for 1856, Art. xxii). His observations, which 

 were conducted for the space of many years, both at Milan and Prague, 

 having given support to the opinion that both the moon and the solar 

 spots occasioned a decennial period of declination, led General Sabine 

 to undertake a very important work. He found that the exclusive in- 

 fluence of the sun on a decennial period, previously examined in rela- 

 tion to Toronto in Canada, by the employment of a peculiar and very 

 exact form of calculation, may be recognised in all the three elements 

 of terrestrial magnetism (Phil. Trans, for 1856, p. 861), as shown by 

 the abundant testimony of hourly observations onrried on for a course 

 of eight years at Hobart Town, from January 1841 to December 1848. 

 Thus both hemispheres furnished the same result as to the operation 

 of the sun, as well as the certainty " that the lunar-diurnal variation 

 corresponding to different years shows no conformity to the inequality 

 manifested in those of the solar-diurnal variation. The earth's induc- 

 tive action, reflected from the moon, must be of a very little amount." 

 (Sabine, in the Phil. Tr. for 1857, Art. i, p. 7, and in bl>e Proceedings 

 of the Royal Soc. vol. viii, No. 20, p. 404). The magnetic portion of 

 this volume having been printed almost three years ago, it seemed 

 especially necessary, with reference to a subject which has so long 

 been a favourite one with me, that I should supply what was wanting 

 by some additional remarks. 



