which, during the period of the greatest drought, from December to March, had been almost constantly in the day-time from 1·7 to 2 lines to Volta’s electrometer, becomes extremely variable after March. During whole days it appears null, and again for some hours the pith-balls of the electrometer diverge from three to four lines. The atmosphere, which in the torrid as in the temperate zone is generally in a state of positive electricity, passes alternately, in the course of eight or ten minutes, to a negative state. The rainy season is that of thunder-storms. The storm rises in the plains two hours after the sun passes through the meridian, and therefore shortly after the period of the maximum of the diurnal heat in the tropics. In the inland districts it is exceedingly rare to hear thunder at night or in the morning--nocturnal thunder-storms being peculiar to certain valleys of rivers which have a particular climate.” The substance of the explanation of the preceding phenomena, by the philosophic writer of the statement, may be briefly given: The season of rains and thunder in the northern equinoctial zone coincides with the passage of the sun through the zenith of the place, the cessation of the breezes or north-east winds, and the frequency of calms and furious currents of the atmosphere from the south-east and south-west, accompanied with a cloudy sky. While the breeze from the north-east blows, it prevents the atmosphere from being saturated with moisture. The hot and loaded air of the torrid zone rises, and flows off again toward the poles, while inferior currents from these last, bringing drier and colder strata, take the place of the ascending columns. In this manner, the humidity--being prevented from accumulating--passes off toward the temperate and colder regions, so that the sky is always clear. When the sun, entering the northern signs, rises toward the zenith, the breeze from the north-east softens, and at length ceases; this being the season at which the difference of temperature between the tropics and the contiguous zone is least. The column of air resting on the equinoctial zone becomes replete with vapors, because it is no longer renewed by the current from the pole: clouds form in this atmosphere, saturated and cooled by the effects of radiation and the dilatation of the ascending air, which increases its capacity for heat in proportion as it is rarefied. Electricity accumulates in the higher regions, in consequence of the formation of the vesicular vapors, the precipitation of which is constant during the day, but generally ceases at night. The showers are more violent and accompanied with electrical explosions, shortly after the maximum of the diurnal heat. These phenomena continue until the sun enters the southern signs, when the polar current is reëstablished, because the difference between the heat at the equinoctial and temperate regions is daily increasing. The air of the tropics being thus renewed, the rains cease,