419 



should be made simultaneously at all stations, at short intervals of 

 time, for a certain number of hours and at fixed periods of the year, 

 precisely similar to the plan which has been recommended and 

 adopted by Sir John Herschel with reference to observations of the 

 barometer and thermometer. 



Referring in terms of commendation to the magnetical observa- 

 tions which have originated in this country, M. de Humboldt ex- 

 presses his wish that such observations may, by the adoption of an 

 uniform plan, and by connecting them with the observations now in 

 progress on the continent of Europe and of Northern Asia, be ren- 

 dered more proper for the manifestation of great physical laws. He 

 then enters into a historical detail of the establishment of stations 

 for magnetical observations, stating the important results obtained 

 by MM. Arago and Kupffer by means of simultaneous observations, 

 which appear to establish the isochronism of the perturbations of 

 the needle at Paris and Kasan, stations separated by 47° of longi- 

 tude. Under the patronage of the Governments of France, of Prus- 

 sia, of Denmark, and of Russia, magnetical observatories have been 

 established at Paris, at Berlin, in the mines of Freyberg, at Copen- 

 hagen, in Iceland, at St. Petersburg, Kasan, Moscow, Barnoul at 

 the foot of the Altai Chain, Nertschinsk near the frontiers of China, 

 even at Pekin, and at NicolajefF in Crimea. 



M. de Humboldt states that the lines representing the horary va- 

 riations at Berlin, Freyberg, Petersburg, and NicolajefF affect paral- 

 lelism, notwithstanding the great separation of the stations and the 

 influence of extraordinary perturbations ; that this, however, is not 

 invariable, since even at small distances, for example, at Berlin and 

 in the mines of Freyberg, one of the needles may show considerable 

 perturbations, while the other continues that regular course which 

 is a function of the solar time of the place. 



The epochs at which it had been proposed that simultaneous ob- 

 servations should be made at all stations were, 



20th and 21st of March 

 4th and 5th of May, 

 21st and 22nd of June, 

 6th and 7th of August, 

 23rd and 24th of September, 

 5th and 6th of November, 

 21st and 22nd of December, „ 



from 4 o'clock in the morning 

 of the first day, until midnight of 

 the second, observing, at least 

 hourly, night, and day, at each 

 magnetic station. 



But as many observers have considered these as too near to each 

 other, the observations most to be insisted upon are those at the 

 times of the solstices and equinoxes. 



England from the times of Gilbert, Graham, and Halley to the 

 present, observes M. de Humboldt, has afforded a copious collec- 

 tion of materials, adapted to the discovery of the physical laws which 

 govern the changes of the variation, whether at the same place, ac- 

 cording to the hours of the day and the seasons of the year, or at 

 different distances from the magnetic equator and from the lines of 

 no variation. After adverting to the continued observations of 



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