44 Baron Humboldt on advancing the Knonsoledge 



placed in a glass frame, and directed towards a very distant 

 meridian mark, the divisions of which, illuminated during the 

 night, indicated even six or seven seconds of horary variation. 

 In verifying the habitual regularity of a nocturnal period^ 

 I was struck with the frequency of the perturbations, espe- 

 cially of oscillations the amplitude of which extended beyond 

 all the divisions of the scale, and which occurred repeatedly 

 at the same hours before sunrise, and the violent and ac- 

 celerated movements of which could not be attributed to any 

 accidental mechanical cause. These vagaries of the needle, the 

 almost periodical return of which has recently been confirmed 

 by Mr. Kupffer in the narration of his Travels in the Caucasus, 

 appeared to me the effect of a reaction of the interior of the 

 earth towards the surface; I should venture to say, of magnetic 

 storms, which indicate a rapid change of tension. From that 

 time it has been my desire to establish on the east and west 

 of the meridian of Berlin apparatus similar to my own, in 

 order to obtain corresponding observations made at great di- 

 stances and at the same hours ; but the political tempest of 

 Germany, and my hasty departure for France, whither I was 

 sent by the Government, delayed for a length of time the ex- 

 ecution of this project. Fortunately my illustrious friend 

 M. Arago, after his return from the coasts of Africa and the 

 prisons of Spain, undertook, I think about the year 1818, a 

 series of observations upon magnetic declinations at the Ob- 

 servatory of Paris, which, made daily at intervals uniformly 

 fixed, and continued upon the same plan to the present day, 

 are considered, with regard to their number and mutual con- 

 nexion, superior to everything that has been attempted in 

 this kind of physical investigations. Gambey's apparatus, 

 which is employed, is of perfect execution. Provided with 

 micrometers and microscopes, it may be employed with more 

 certainty and convenience than Prony's instrument, which is 

 attached to a strong magnetized bar of 20j inches in length. 



During the progress of these observations M. Arago has 

 discovered, and proved by numerous examples, a phsenomenon 

 which differs essentially from the observation made by Prof. 

 Hiorter at Upsal in IHl. He has discovered not only that 

 the Aurora horeales disturb the regular progress of the horary 

 declinations there when they are not visible, but also that 

 early in the morning, often ten or twelve hours before the lu- 

 minous phaenomenon is developed in a very distant place, its 

 appearance is announced by the particular form presented by 

 the curve of the diurnal variations, that is, by the value of the 

 maxima of elongation of the morning and night. Another new 

 fact was manifested in the perturbations. Mr. Kupffer having 



