146 PBOPAGATION OF AEBIAL ACTION. 



the season of drought, from December to March, had been 

 constantly, in the day-time, from 1-7 to 2 lines, becomes 

 extremely variable from the month of March. It appears 

 nil during whole days ; and then for some hours the pith- 

 balls diverge three or four lines. The atmosphere, which 

 is generally, in the torrid as well as in the temperate 

 zone, in a state of positive electricity, passes alternately, 

 for eight or ten minutes, to the negative state. The season 

 of rains is that of storms; and yet a great number of 

 experiments made during three years, prove to me that it 

 is precisely in this season of storms we find the smallest 

 degree of electric tension in the lower regions of the atmo- 

 sphere. Are storms the effect of this unequal charge of 

 the different superincumbent strata of air? "What pre- 

 vents the electricity from descending towards the earth, in 

 air which becomes more humid after the month of March ? 

 The electricity at this period, instead of being diffused 

 throughout the whole atmosphere, appears accumulated on 

 the exterior envelope, at the surface of the clouds. Accor- 

 ding to M. Gray-Lussac it is the formation of the cloud itself 

 that carries the fluid toward its surface. The storm rises in 

 the plains two hours after the sun has passed the meridian ; 

 consequently a short time after the moment of the maxi- 

 mum of diurnal heat within the tropics. It is extremely rare 

 in the islands to hear thunder during the night, or in the 

 morning. Storms at night are peculiar to certain valleys of 

 rivers, having a pecul : ar climate. 



"What then are the causes of this rupture of the equili- 

 brium in the electric tension of the air ? of this continual 

 condensation of the vapours into water ? of this interruption 

 of the breezes ? of this commencement and duration of the 

 rainy seasons? I doubt whether electricity have any in- 

 fluence on the formation of vapours. It is rather the for- 

 mation of these vapours that augments and modifies the 

 electrical tension. North and south of the equator, storms 

 or great explosions take place at the same time in the 

 temperate and in the equinoctial zone. Is there an action 

 propagated through the great aerial ocean from the tem- 

 perate zone towards the tropics 1 How can it be con- 

 ceived, that in that zone where the sun rises constantly 

 to so great a height above the horizon, its passage through 





