is but very recently, that pains had been taken with some success, to solve this grand problem of subterraneous meteorology. The stony strata, that form the crust of our planet, are alone accessible to our examination; and we now know, that the mean temperature of these strata varies not only with the latitudes and the heights, but that, according to the position of the several places, it performs also, in the space of a year, regular oscillations round the mean heat of the neighbouring atmosphere. We are already far from that period, when men were surprised to find, under other zones, the heat of grottoes and wells differing from that, which is observed in the caves of the ob servatory at Paris. The same instrument, which in those caves marks 12°, rises in the subterraneous caverns of the island of Madeira, near Funchal*, to 16.2°; in Joseph's Well, at Cairo †, to 21.2°; in the grottoes of the Island * At Funchal (lat. 32° 37') the mean temperature of the air is 20-4°. This is so much the more probable, as Mr. Escolar finds at Santa Cruz, in Teneriffe, 21.8° (Cavendish, in the Philosoph. Trans. for 1778, p. 392). We shall hereafter recur again to this remarkable difference between the caves in the island of Madeira and the surrounding at mosphere. + At Cairo (lat. 39° 2′) the mean temperature of the air is 22.4°, according to Nouet. of Cuba* to 22 or 23°. This increase is nearly in proportion to that of the mean temperature of the atmosphere, from the latitude of 48 to the tropics. We have just seen, that in the Cueva del Guacharo, the water of the river is nearly 2° colder than the ambient air of the cavern. The water, whether in filtering through the rocks, or in running on stony beds, assumes without doubt the temperature of these beds. The air contained in the grotto, on the contrary, is not in repose; it communicates with the atmosphere without. Though under the torrid zone, the changes of the exterior temperature are exceedingly small currents are formed, which modify periodically the internal air. It is consequently the temperature of the waters, that of 16.8°, which we might look upon as the temperature of the earth in those mountains, if we were sure, that these waters do not descend with rapidity from more elevated neighbouring mountains. It follows from these observations, that, when we cannot obtain results perfectly exact, we find at least under each zone certain numbers, which indicate the maximum and minimum. At Caripe, in the equinoxial zone, at 500 toises of * Obs. Astr. Tom. i, p. 134. The mean temperature of the air at the Havannah, according to Mr. Ferrer, is 25.6°. height, the mean temperature of the globe is not below 16.8°, which was what the water of the subterranean river indicated. We can even prove, that this temperature of the globe is not above 19°; since the air of the cavern, in the month of September, was found at 18.7°. As the mean temperature of the atmosphere, in the hottest month, does not exceed 19.5°*, it is probable, that a thermometer, placed in the open air in the grotto, would not rise higher than 19° in any season of the year. These results, as well as many others, which we have recorded in this journey, seem of little importance, on viewing them singly; but, if we compare them with the observations recently made by Messrs. von Buch and Wahlenberg, under the polar circle, they throw light on the economy of nature in general, and the equilibrium of temperature, toward which the air and earth are continually tending. It is no longer doubtful, that in Lapland the stony crust of the globe is three or four degrees above the mean temperature of the atmosphere. Does the cold, which perpetually reigns in the abysses of the Equinoc The mean temperature of the month of September at Caripe is 18.5°; and on the coast of Cumana, where we had opportunities of collecting a great number of observations, the mean heat of the warmest months differs only 1.8° from that of the coldest. tial Ocean, and which is the effect of the polar currents, produce, under the tropics, a sensible diminution of the temperature of the earth? Is this temperature below that of the atmosphere? This we mean to examine hereafter, when we have collected more facts in the high regions of the Cordillera of the Andes. CHAPTER VIII. Departure from Caripe.-Mountain and Forest of Santa Maria.-Mission of Catuaro.-Port of Cariaco. THE days we passed at the convent of the Capuchins, in the mountains of Caripe, glided hastily away, though our manner of living was simple and uniform. From sunrise to nightfall we traversed the forests and neighbouring mountains, to collect plants, of which we had never made a more considerable harvest. When the winter rains prevented us from undertaking distant excursions, we visited the huts of the Indians, the conuco of the community, or those assemblies, in which the alcaides settle every evening the labours of the succeeding day. We returned to the monastery, only when the sound of the bell called us to partake in the refectory the repast of the missionaries. Sometimes, very early in the morning we followed them to the church, to attend the doctrina, that is to say, the religious instruction of the Indians. It is an undertaking at least very difficult, to speak |