3^^ Ijetter from P'bn Humboldt lo Lalande, 



ology of plants and animals; and under the latitude of lo* 

 it is impoflible to labour fo inceflantly as under 49"". I chofe 

 lather to make a few obfervations with accuracy, than a great 

 many imperfedl^ones; and to infert them with great minute- 

 nefs in my journals, that, in cafe I fhould die in the courfe 

 of my travels, no doubt might remain in regard to their 

 cxaftnefs. 



In the two papers which I tranfmitted to Delambre, you 

 will find my oblervations made in Europe with Borda's new 

 inclmator'ttim, I found by it, that local circumftances have 

 a greater influence on the inclination of the ma<Tnetic needle 

 than on its declination ; and that no connexion fcems to 

 exift between the fituation of ihe place of obfervation ard the 

 inclination. This I find confirmed in the new world in the 

 interior of New Andalufia, and therefore the obfervations 

 made by Nonet in Egypt feem to be cftabliflied. The de- 

 clination, however, is aflfefted by local caufes, but much lefs : 

 at fea they are much more regular, and the variations are 

 much more uniform. 



I have here given you my obfervations of the inclination 

 only, which are true to 15'. During calms I obtained them 

 at fea with more accuracy, and the periods of the vibrations 

 of the needle could be determined very exaftly. If the fame 

 number is counted in the fame time during five or fix repeated 

 trials, and if this is ftill the cafe when the infi:rument is 

 moved from its place, the refults, in my opinion, may be 

 confidered as correct. Though calms are not uncommon 

 between the tropics, during the courfe of forty days I was 

 able to make only ten very accurate obfervations. 



Magnetic Power. 



K\Hnl)cr ill Vihidti'-m 



in Ten Mimires. 



245 

 240 



»45 

 244 

 243 



24? 

 240 



235 

 240 



240 



23/ 

 242 

 242 



239 



236 

 239 



a -,4 

 229 



■«J7 



In 



