On the conji'itucnt Paris of the Atmofphere. 'i^*j 



dry and ferene weather. After great rain the eudrometer in- 

 dicates in atmofpheric air only o'264, and 0*359 of oxygen. 

 But when the blue fky appears, the eudiometer marks 0*284 

 of oxygen, and as far as 0*290. The experiments of Read 

 feem to announce a combination between oxygen and elec- 

 tricity; but we are ftill ignorant whether the air being charged 

 with the electric matter has any influence on its purity. Buch 

 collefted the air of the Gifberg at an elevation of 3890 feet, 

 and Humboldt found this air exceedingly impure. It appeared 

 by the eudiometer that it contained 0*026 lefs of oxygen than 

 that of the plain ; which confirms what we before knew, that 

 the air on high mountains is more impure than that found 

 at a lefs elevation. The purity of the air varies to fuch a 

 degree, that the author faw the eudiometer announce, be- 

 tween April and November 1797, from 0*290 of oxygen to 

 0*235. But, does atmofpheric air contain only oxygen, azot, 

 and carbonic acid ? The author thinks it probable that it 

 contains alfo a portion of hydrogen, which combines with 

 the azot, and which we have no means of dete6ling. Hum- 

 boldt collefted air in the crater of the peak of Teneriffe, at 

 the height of 1904 toifes, and found in it only o*i'9 of oxy- 

 gen. It mull be obferved that there is no longer any erup- 

 tion from this crater. The pure air of the plain at the bot- 

 tom of the peak contains 0*278 of oxygen. The air at fea 

 in the latitude of 10° 30' contained more than 0*30 of oxy- 

 gen. This obfervation fliows that the air at fea contains 

 more oxygen than that at land *, 



METEOROLOGV. 



Bouvard continues to make meteorological obfervations 

 with great accuracy. He has found the variation of the 

 needle at Paris to be 32^ 15', and the dip 70^ 2^. Coulomb 

 employs a new procefs to find the dip of the needle, which 

 at Paris he eftimates at 6H^ 10'. 



Humboldt has made interelting obfervations refpefting the 

 magnetic needle. The following is the rdult of thofc in 



■' For other important infornnation conne6led with this branch, fee 

 Dr. Van Mons's letter in our lall, and Dr. Girtanncr's in our prelent, 

 Wumbcr. 



rciiard 



