1837.] 



Report on Terrestrial Magnetism, 



22S 



After his return from the equinoctial regions of America, M. de 

 Humboldt, in the years 1806 and 1807, entered upon a careful and 

 minute examination of the course of the diurnal variation of the 

 needle. He was struck, he informs us, in verifying the ordinary regu- 

 larity of the nocturnal period, with the frequency of perturbations, 

 ana, above all^ of those oscillations, exceeding the divisions of his 

 scale, which were repeated frequently at the same hours before sun- 

 rise. These eccentricities of the needle, of which a certain periodi- 

 city has been con-firmed by Kupffer, appeared to M„ de Humboldt 

 to be the effect of a re-action from the interior towards the surface of 

 the globe — he ventures to say of " magnetic-storms" — which indicated 

 a rapid change of tension. From that time he was anxious to esta- 

 blish to the east and to the west of the meridian of Berlin, apparatus 

 similar to his own, in order to obtain corresponding observations made 

 at great distances at the same hours, but was for a long period pre- 

 vented putting his plan into execution by the disturbed state of Ger- 

 many and his departure for France. 



The Baron de Humboldt and MM. Arago and Kupffer having, by the 

 eo-operation of many zealous observers, succeeded in establishing per- 

 manent magnetic stations extending from Paris to China, M. de Hum- 

 boldt solicits, through his Royal Highness the President, the powerful 

 influence of the Royal Society in extending the plan, by the establish- 

 ment of new stations. The plan which he proposes, and which has 

 been successfully carried into execution over a large portion of the 

 north-eastern continent, is, that magnetical observations, whether of 

 the direction of the horizontal and inclined needles, or fur the deter- 

 mination of the variations of the magnetic force, 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 ther- 

 mometer. 



Referring in terms of commendation to the magnetical observations 

 which have originated in this country, M. de Humboldt expresses 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 rendered more proper 

 for the. manifestation of great physical laws. He then enters into an 

 historical detail of the establishment of stations for magnetical obser- 

 vations, stating the important results obtained by MM. Arago and 

 Kupffer by means of simultaneous observations, which appear to esta- 

 blish the isochronism of the perturbations of the needle at Paris and 

 Kasan, stations separated by 47° of longitude. Under the patronage 

 of the Governments of France, of Prussia, of Denmark, and of Russia* 



