102 



THE ATMOSPHERE. 



withdrawing water from the atmosphere. With 

 the parched levels of Cumana, Coro, and Cea- 

 ra, in North Brazil, the deluges of rain which 

 fall in other districts of tropical countries con- 

 trasts strongly : for example, in Havana, where 

 observations carried on for six years by Ramon 

 de la Sarga show the mean annual fall of rain 

 to amount to 102 Parisian inches — four or five 

 times as much as it is in Paris or Geneva(^"). 

 On the slopes of the Andes, the quantity of 

 rain that falls, like the temperature, diminishes 

 with the height(3"). It was found by my com- 

 panion in my South American journey, M. Gal- 

 das, of Santa Fe de Bogota, not to exceed 37 

 inches at a height of 8200 feet, which is but 

 little more than the quantity that falls on some 

 of the west coasts of Europe. At Quito, when 

 the temperature was from 12° to 13° C, Bous- 

 singault sometimes saw Saussure's hygrome- 

 ter recede to 26° ; and in his great aerostatic 

 ascent Gay Lussac saw the same instrument 

 at 25° -3, his elevation at the time being 6600 

 feet, and the temperature of the air 4° 6 C. 

 The greatest degree of dryness yet observed in 

 a low country was seen by Gustavus Rose, 

 Ehrenberg, and myself, between the valleys of 

 the Irtisch and Obi, in Northern Asia. In the 

 Platowskaja Steppe, after the south-west wind 

 had been long blowing from the interior of the 

 continent, the temperature of the air being 

 23° -7 C., we found the dew-point 4° -3 below 

 the freezing-point. The air only contained -^^^ 

 of watery vapour(3"). Several able observers, 

 Kaemtz, Bravais, and Martins, have of late 

 years called in question the great degree of 

 dryness of the mountain air, which seemed to 

 follow from Saussure's observations among the 

 Alps, and my own among the heights of the 

 Cordilleras. The relative moistness of the air 

 in Zurich was contrasted with that of the air 

 of the Faulhorn, a mountain which indeed could 

 only be called high in Europe(^'8). The moist- 

 ure with which the peculiar species of large- 

 flowered, myrtle-leaved Alpine shrubs are al- 

 most perpetually bedewed in the region of the 

 Paramos of the tropical Andes, between 11,000 

 and 12,000 feet above the sea level, and not far 

 from the line where snow begins to fall, does 

 not, however, necessarily imply a great abso- 

 lute moistness of the air in this region ; like 

 the frequent fogs in the beautiful plateau of 

 Bogota, it only proclaims the frequency of pre- 

 cipitations. Banks of fog at these heights form 

 and disappear several times in the course of 

 an hour when the air is calm ; such rapid chan- 

 ges characterize the lofty plateaus and paramos 

 of the Andes. 



The ELECTRICITY OF THE ATMOSPHERE, Whcth- 



er considered in the lower regions or in the 

 cloudy canopy aloft, viewed problematically in 

 its silent periodical diurnal progression, or in 

 the brilliant and noisy explosions of the thun- 

 der-storm, stands in manifold relationship with 

 all the phenomena of thermal distribution, of 

 atmospheric pressure and its disturbances, of 

 hydrometeors, and apparently also of the mag- 

 netism of the outer crust of the earth. It ex- 

 erts a most powerful influence upon the whole 

 of the animal and vegetable world, and this not 

 merely through the meteorological processes, 

 precipitations of watery vapour, of acids, or of 

 ammoniacal compounds, which it occasions, 



but also immediately as the electrical force, 

 that force which excites the nerves and occa- 

 sions or assists the circulation of the juices. 

 This is not the place to renew the contest in 

 regard to the source of the electricity of the 

 serene sky, which has at one time been ascri 

 bed to the evaporation of impure fluids, i. e. flu- 

 ids loaded with earths and salts(3"), at another 

 to the growth of vegetab]es(3'*°), or other chem- 

 ical decompositions proceeding on the surface 

 of the earth, to the unequal distribution of heat 

 in the different strata of the atmosphere(3®^), 

 finally, according to Peltier's able inquiries(^^'), 

 to the influence of a constantly negative charge 

 of the globe. Limited to the results which 

 electrometrical observations, particularly those 

 which the clever arrangement of an electro- 

 magnetical apparatus, first proposed by Colla- 

 don, have given. Physical Cosmography ought 

 to indicate the unquestionable increase of the 

 general positive aerial electricity with the height 

 of the station and freedom from surrounding 

 trees(^«^), its daily ebb and flow (according to 

 Clarke's Dublin experiments, in more intricate 

 periods than Saussure and I had detected), and 

 its differences according to season, distance 

 from the equator, and the continental or oceanic 

 nature of the surface. 



If the electrical equilibrium, on the whole, be 

 less disturbed where the atmosphere is resting 

 on the sea than on the land, it is the more re- 

 markable to observe how small clusters of isl- 

 ands surrounded by an extensive ocean act 

 upon the state of the atmosphere and give oc- 

 casion to thunder-storms. In fogs, and at the 

 beginning of falls of snow, I have in the course 

 of a long series of observations seen the pre- 

 vious permanent vitreous, change suddenly into 

 the resinous electricity, and these alternate re- 

 peatedly, as well in the plains of the frigid zone 

 as under the tropics in the Paramos or Alpine 

 wildernesses of the Cordilleras between 10,000 

 and 12,000 feet high. The alternate transition 

 was in all respects similar to that which the 

 electrometer had shown shortly before during 

 the continuance of a thunder-storm(^^*). When 

 the vesicles of vapour have become aggregated 

 into clouds with determinate outlines, the elec- 

 trical tension of the outer layer or surface(^**) 

 upon which the electricity of the insulated ve- 

 sicular vapour overflows, increases with the 

 measure of the condensation. Slate-gray col- 

 oured clouds, according to Peltier's Paris ex- 

 periments, have resinous, white, rose, and 

 orange-coloured clouds, have vitreous electri- 

 city. Thunder clouds not only involve the 

 highest summits of the Andes, (I have myself 

 observed the vitrifying effects of lightning on 

 one of the rocky crags which rise from the cra- 

 ter of the Volcano of Toluca, 14,300 feet high), 

 but storm clouds have been measured, which 

 were floating over low lands in the temperate 

 zone, at a vertical height of 25,000 feet(^^*). 

 Occasionally, however, the thundering and 

 lightning stratum of cloud descends to an alti- 

 tude of five, and even of three thousand feet 

 from the ground. 



According to Arago's experiments, the most 

 comprehensive we yet possess upon this diffi- 

 cult portion of meteorology, there are dischar- 

 ges of lightning of three kinds : zig-zag or fork- 

 ed lightnings, sharply defined on their edges ; 



