The Quantity Of Light Received On That Part Of The Sea Where The Visual Ray Terminates; And The Extinction Of The Reflected Light During Its Passage Through The Intermediate Strata Of Air.

It may happen, notwithstanding the serenity of the sky and the transparency of the atmosphere, that the ocean is

Feebly illuminated at thirty or forty leagues' distance; or that the strata of air nearest the earth may extinguish a great deal of the light, by absorbing the rays that traverse them.

The rounded peak, or western dome of the Silla, concealed from us the view of the town of Caracas; but we distinguished the nearest houses, the villages of Chacao and Petare, the coffee plantations, and the course of the Rio Guayra, a slender streak of water reflecting a silvery light. The narrow band of cultivated ground was pleasingly contrasted with the wild and gloomy aspect of the neighbouring mountains. Whilst contemplating these grand scenes, we feel little regret that the solitudes of the New World are not embellished with the monuments of antiquity.

But we could not long avail ourselves of the advantage arising from the position of the Silla, in commanding all the neighbouring summits. While we were examining with our glasses that part of the sea, the horizon of which was clearly defined, and the chain of the mountains of Ocumare, behind which begins the unknown world of the Orinoco and the Amazon, a thick fog from the plains rose to the elevated regions, first filling the bottom of the valley of Caracas. The vapours, illumined from above, presented a uniform tint of a milky white. The valley seemed overspread with water, and looked like an arm of the sea, of which the adjacent mountains formed the steep shore. In vain we waited for the slave who carried Ramsden's great sextant. Eager to avail myself of the favourable state of the sky, I resolved to take a few solar altitudes with a sextant by Troughton of two inches radius. The disk of the sun was half-concealed by the mist. The difference of longitude between the quarter of the Trinidad and the eastern peak of the Silla appears scarcely to exceed 0 degrees 3 minutes 22 seconds.* (* The difference of longitude between the Silla and La Guayra, according to Fidalgo, is 0 degrees 6 minutes 40 seconds.)

Whilst, seated on the rock, I was determining the dip of the needle, I found my hands covered with a species of hairy bee, a little smaller than the honey-bee of the north of Europe. These insects make their nests in the ground. They seldom fly; and, from the slowness of their movements, I should have supposed they were benumbed by the cold of the mountains. The people, in these regions, call them angelitos (little angels), because they very seldom sting. They are no doubt of the genus Apis, of the division melipones. It has been erroneously affirmed that these bees, which are peculiar to the New World, are destitute of all offensive weapons. Their sting is indeed comparatively feeble, and they use it seldom; but a person, not fully convinced of the harmlessness of these angelitos, can scarcely divest himself of a sensation of fear. I must confess, that, whilst engaged in my astronomical observations, I was often on the point of letting my instruments fall, when I felt my hands and face covered with these hairy bees. Our guides assured us that they attempt to defend themselves only when irritated by being seized by their legs. I was not tempted to try the experiment on myself.

The dip of the needle at the Silla was one centesimal degree less than in the town of Caracas. In collecting the observations which I made during calm weather and in very favourable circumstances, on the mountains as well as along the coast, it would at first seem, that we discover, in that part of the globe, a certain influence of the heights on the dip of the needle, and the intensity of the magnetical forces; but we must remark, that the dip at Caracas is much greater than could be supposed, from the situation of the town, and that the magnetical phenomena are modified by the proximity of certain rocks, which constitute so many particular centres or little systems of attraction.* (* I have seen fragments of quartz traversed by parallel bands of magnetic iron, carried into the valley of Caracas by the waters descending from the Galipano and the Cerro de Avila. This banded magnetic iron-ore is found also in the Sierra Nevada of Merida. Between the two peaks of the Silla, angular fragments of cellular quartz are found, covered with red oxide of iron. They do not act on the needle. This oxide is of a cinnabar-red colour.)

The temperature of the atmosphere varied on the summit of the Silla from eleven to fourteen degrees, according as the weather was calm or windy. Every one knows how difficult it is to verify, on the summit of a mountain, the temperature, which is to serve for the barometric calculation. The wind was east, which would seem to prove that the trade-winds extend in this latitude much higher than fifteen hundred toises. Von Buch had observed that, at the peak of Teneriffe, near the northern limit of the trade-winds, there exists generally at the elevation of one thousand nine hundred toises, a contrary current from the west. The Academy of Sciences recommended the men of science who accompanied the unfortunate La Perouse, to employ small air-balloons for the purpose of ascertaining at sea the extent of the trade-winds within the tropics. Such experiments are very difficult. Small balloons do not in general reach the height of the Silla; and the light clouds which are sometimes perceived at an elevation of three or four thousand toises, for instance, the fleecy clouds, called by the French moutons, remain almost fixed, or have such a slow motion, that it is impossible to judge of the direction of the wind.

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