124 ANNUAL OF SCIENTIFIC DISCOVERY. 



measure at the surface of the globe, should not be in any degree 

 influenced by the variations in the magnetic conditions of the oxygen 

 of the atmosphere in different seasons and at different hours of the 

 day and night ; but whether that influence be sensible or not, whether 

 it be appreciable by our instruments or inappreciable by them, is a 

 question which yet remains for solution^ by the more minute sifting of 

 the accumulated facts which are now undergoing examination in so 

 many quarters. 



To justify the anticipation that conclusions of the most striking 

 character, and wholly unforseen, may yet be derivable from the 

 materials in our possession, we need only to recall the experience of 

 the last few months, which have brought to our knowledge the exist- 

 ence of what may possibly prove the most instructive, as it is certainly 

 at first sight the least explicable of all the periodical magnetic variations 

 with which we have become acquainted. I refer to the concurrent 

 testimony which observations at parts of the globe the most distant 

 from each other bear to the existence of a periodical variation or 

 inequality, affecting alike the magnitude of the diurnal variations, and 

 the magnitude and frequency of the disturbances or storms. The 

 cycle or period of this inequality appears to extend to about ten of our 

 years ; the maximum and minimum of the magnitudes affected by it 

 being separated by an interval of about five years, and the differences 

 being much too great, and resting on an induction far too extensive, 

 to admit of uncertainty as to the facts themselves. The existence of 

 a well-marked magnetic period which has certainly no counterpart in 

 thermic conditions, appears to render still more doubtful the supposed 

 connexion between the magnetic and calorific influences of the sun. 

 It is not a little remarkable that this periodical magnetic variation is 

 found to be identical in period and in epochs of maxima and minima 

 with the periodical variation in the frequency and magnitude of the 

 solar spots which Mr. Schwabe has established by twenty-six years of 

 unremitting labor. From a cosmical connexion of this nature, suppos- 

 ing it to be finally established, it would follow, that the decennial period 

 which we measure by our magnetic instruments is, in fact, a solar period, 

 manifested to us also by the alternately increasing and decreasing 

 frequency and magnitude of obscurations on the surface of the solar 

 disc. May we not have in these phenomena the indication of a cycle 

 or period of secular change in the magnetism of the sun, affecting visibly 

 his gaseous atmosphere or photosphere, and sensibly modifying the 

 magnetic influence which he exercises on the surface of our earth. 



We recognise in terrestrial magnetism the existence of a poAver 

 present everywhere at the surface of our globe, and producing every- 

 where effects indicative of a systematic action ; but of the nature of 

 this power, the character of its laws, and its economy in creation, we 

 have as yet scarcely any knowledge. The apparent complexity of 

 the phenomena at their first aspect may reasonably be ascribed to our 

 ignorance of their laws, which we shall doubtless find, as we advance 

 in knowledge, to possess the same remarkable character of simplicity 

 which calls forth our admiration in the laws of molecular attraction. 



