of Terrestrial Magiietism. 43 



Mr. Kupffer, and myself have succeeded in the last eight years 

 in extending these researches over a very considerable part 

 of the northern hemisphere. Permanent magnetic stations be- 

 ing now established from Paris to China, following towards 

 the east the parallels from 40° to 60°, I feel myself justified 

 insoliciting, through the intervention of Your Royal Highness, 

 the powerful cooperation of the Royal Society of London, to 

 sanction this enterprise, and also to promote its success by the 

 establishment of new stations, as well in the vicinity of the 

 magnetic equator as in the temperate part of the southern 

 hemisphere. 



An object which is equally important whether it be consi- 

 dered in connexion with the physics of the earth or the im- 

 provement of nautical science, has a double claim upon the 

 attention of a Society, which has from its commencement, with 

 constantly increasing success, cultivated the vast field ot the 

 exact sciences. Our information respecting the progressive 

 development of the knowledge which we possess oi terrestrial 

 magnetism must be indeed imperfect, if we are ignorant of the 

 numerous valuable observations which have been made at dif- 

 ferent epochs^ and are still being made, in the British isles, 

 and in various parts of the equinoctial zone subject to the 

 same empire. Our present object is to render these observa- 

 tions more useful, that is, better adapted to manifest great 

 physical laws, by coordinating them according to a uniform 

 plan, and connecting them with the observations now in pro- 

 gress upon the continent of Europe and Northern Asia. 



Having been much occupied during my travels in the equi- 

 noctial regions of America, during the years 1799 — ISO't, with 

 the phaenomena of the intensity of the magnetic forces, and the 

 inclination and declination of the magnetic needle, on my re- 

 turn to my own country I conceived the design of examining 

 the progress of the horary variations of the declination^ and 

 the perturbations to which it is liable, by employing a method 

 which, I believe, has never yet been followed upon an exten- 

 sive scale. In a large garden at Berlin, during the years 

 J 806 and 1807, particularly at the period of the equinoxes 

 and solstices, I measured the angular alterations of the mag- 

 netic meridian, at intervals of an hour, often of half an hour, 

 without interruption during four, five, and six days, and as 

 many nights. Mr. Oltmanns, whose numerous calculations of 

 geographical positions have recommended him to the notice 

 of astronomers, kindly shared with me the fatigues of these 

 labours. The instrument which we employed was a magnetic 

 telescope [lunette aimantce) of Prony, capable of being reversed 

 upon its axis, suspended according to the method of Coulomb^ 



G2 



