461 



superposition of two undulations having the same period but different 

 amplitudes, and different epochal times ; and that by attending to 

 this principle, many of the most complex phenomena, such as that of 

 a double maximum and minimum, with the occurrence of a nightly 

 as well as a daily movement, are explained in a satisfactory manner. 



The discussion of the observations already accumulated has further 

 brought into view, and in the opinion of your Committee fully esta- 

 blished, the existence of a very extraordinary periodicity in the extent 

 of fluctuation of all the magnetic elements, and in the amplitude and 

 frequency of their irregular movements especially, which connects 

 them directly with the physical constitution of the sun, and with the 

 periodical greater or less prevalence of spots on its surface the 

 maxima of the amount of fluctuation corresponding to the maxima 

 of the spots, and these again with those of the exhibitions of the 

 Aurora Borealis, which appears also to be subject to the same law of 

 periodicity ; a law, which as it does not agree with any of the other- 

 wise known solar, lunar, or planetary periods, may be considered as, 

 so to speak, personal to the sun itself. And thus we find ourselves 

 landed in a system of cosmical relations, in which both the sun and 

 the earth, and probably the whole planetary system, are implicated. 



That the sun acts in influencing the earth's magnetism in some 

 other manner than by its heat, seems to be rendered very probable 

 by several features of this inquiry, and the idea of a direct magnetic 

 influence exterior to the earth, is corroborated by the discovery of a 

 minute fluctuation in the magnetic elements, having for its period 

 not the solar but the lunar day, and therefore directly traceable to 

 the action of the moon. The detection of this fluctuation by M. 

 Kreil, from a discussion of the Prague observations, has been con- 

 firmed by the evidence afforded by those of our Colonial observatories, 

 and appears to be placed beyond all question by the recent deductions 

 for the horizontal force and the declination extending over three years 

 of observation at the Cape of Good Hope, which General Sabine has 

 submitted for your Committee's inspection, and in both which the 

 fluctuations in question emerge in a very satisfactory manner, and 

 one calculated to give a high idea of the precision of which such 

 determinations are susceptible, when it is considered that the total 

 amplitude of oscillation due to this cause in the direction of the Cape- 

 needle is only about 16" of angle. 



VOL. ix. 2 i 



