MAGNETIC VARIATION. &5 



If, as Sabine has shown, the magnetism of the sun is 

 manifested by an increase in the terrestrial force when the 

 earth is nearest to that luminary, it is the more striking 

 that, according to Kreil's very thorough investigations of the 

 magnetic influence of the moon, the latter should hitherto not 

 have been perceptible, either during the different lunar 

 phases, or at the different distances assumed by the satellite 

 in relation to the earth. The vicinity of the moon does not 

 appear, when compared with the sun, to compensate in this 

 respect for the smallness of its mass. The main result of 

 the investigation, in relation to the magnetic influence of the 

 earth's satellite, which, according to Melloni, exhibits only a 

 trace of calorification 8 *, is that the magnetic declination 

 in our planet undergoes a regular alteration in the course of 

 a lunar day, during which it exhibits a twofold maximum 

 and a twofold minimum. Kreil very correctly observes, 

 "that if the moon exerts no influence on the temperature on 

 the surface of our earth (which is appreciable by the ordi- 

 nary means of measuring heat), it obviously cannot in this 

 way effect any alteration in the magnetic force of the earth ; 

 but if, notwithstanding, an alteration of this kind is actually 

 experienced, we must necessarily conclude that it is pro- 

 duced by some other means than through the moon's heat." 

 Everything that cannot be considered as the product of a 

 single force must require, as in the case of the moon, that all 

 foreign elements of disturbance should be eliminated, in order 

 that its true nature may be recognized. 



Although hitherto the most decisive and considerable 

 variations in the manifestations of terrestrial magnetism do 

 not admit of being satisfactorily explained by the maxima 

 and minima in the variations of temperature, there can be 

 no doubt that the great discovery of the polar property of 

 oxygen in the gaseous envelope of our earth will, by a more 

 profound and comprehensive view of the process of the 

 magnetic activity, speedily afford us a most valuable assist- 

 ance in elucidating the mode of origin of this process. It 

 would be inconceivable if, amid the harmonious co-operation 

 of all the forces of nature, this property of oxygen and its 

 modification by an increase of temperature, should not par- 



86 Kreil, Einfiuss des Mondes auf die Magnetisdie Declination, 1852, 

 s. 27, 29, 46. 



