RECTIFICATIONS AND ADDITIONS. 451 



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Although the nearness of the moon in comparison 

 with the sun does not seem to compensate the smallness 

 of its mass, yet the already securely ascertained variation 

 of the magnetic declination in the course of a lunar day, 

 "lunar-diurnal magnetic variation" (Sabine in the 

 Report to the British Association at Liverpool, 1854, 

 p. 11 ; and for Hobarton, Phil. Trans. 1857, art. i. p. 6), 

 incites us perseveringly to continue and extend the 

 researches on the magnetic influences of our satellite. 

 Kreil has the great merit of having pursued this ex- 

 amination with great care from 1839 to 1852 (see his 

 "Abhandlung iiber den Einfluss des Mondes auf die 

 horizontale Componente der magnetischen Erdkraft," in 

 the " Denkschriften der Wiener Akademie der Wiss. 

 math em. naturwiss. Classe, Bd. v. 1853, S. 45 ; and Phil. 

 Trans, for 1856, art. xxii.) As M. Kreil's observations, 

 made during several years at Milan and Prague, led him 

 to believe that the moon causes a decennial declination 

 period similar to that occasioned apparently by the sun- 

 spots, General Sabine was induced to undertake a more 

 extensive investigation, whereby he ascertained that the 

 influence of the sun alone produces a decennial period, 

 which indeed he had already made out for Toronto, in 

 Canada, by the employment of a special and very accu- 

 rate mode of calculation (Phil. Trans. 1856, p. 361). 

 This influence of the sun was also distinctly manifested 

 by the hourly observations, continued during eight years, 

 at Hobarton in Van Diemen Island ; but while, in both 

 hemispheres, the southern as well as the northern, the 



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