NATURAL PHENOMENA OF THE EQUATORIAL REGIONS. 375 



yards] a great deal of hail is formed ; and the atmosphere 

 at this height is commonly charged with negative electri- 

 city. 



It is well known, that the blueness of the sky is deeper Blueness of the 

 in proportion as the air is more dilated. Mr. von 11. thought s y ' 

 he observed, that in general it was more intense under the 

 tropics, than at an equal height in Europe. This he as- 

 cribes to the complete solution of the vapours in the equa- 

 torial atmosphere. On the Andes the blueness was 46° of 

 Saussure's cyanometer. 



The decrease of light is greater in proportion to the den- Light, 

 sity of the strata of the air; accordingly it is much less on 

 the. summits of high mountains. In general the light is 

 much stronger under the tropics, than at equal heights in 

 Europe. This is confirmed by the light reflected from the 

 moon to the Earth in a total eclipse. This intensity of the 

 light probably acts on vegetable productions, and contri- 

 butes to that resinous and aromatic character, which they 

 exhibit on the tops of mountains. Perhaps too it exerts 

 its influence on the nerves; as the inhabitants of Quito 

 have a sensation of faintness, whenever the sun darts his 

 rays on them. 



Bouguer calculated, that the atmosphere, reduced to the Atmosphere, 

 temperature of 0° [32° F.] throughout its whole extent, 

 and to a column of mercury of 76 met. [29*9 in.], would 

 be 7820 met. [8546 yards, or not quite 5 miles] : the ob- 

 servation of the twilight shows, that at 60000 met. [65571 

 yards, or rather more than 37 miles] the air has sufficient 

 density to send us a perceptible light. 



Mr. von H. gives some results of experiments made by Uniformity of 

 him and Mr. Gay-Lussac on the chemical composition of its composition. 

 the atmosphere. From these experiments the component 

 parts of the air are 0*210 of oxigen gas, 0*787 of nitrogen, 

 and 0*003 of carbonic gas. If there be any variation, it 

 appears not to exceed a thousandth part of oxigen ; and 

 Mr. Gay-Lussac found it the same at the height of 7000 

 met. [7650 yards]. 



Of the interesting series of geological observations we 

 can give here but a few particulars. 



The 



