Very Near The Hato The Talcose Slate Becomes Entirely White, And Contains Small Layers Of Soft And Unctuous Graphic Ampelite.* (* Zeichenschiefer.) Some Pieces, Destitute Of Veins Of Quartz, Are Real Granular Plumbago, Which Might Be Of Use In The Arts.

The aspect of the rock is very singular in those places where thin plates of black ampelite alternate with thin, sinuous, and satiny plates of a talcose slate as white as snow.

It would seem as if the carbon and iron, which in other places colour the primitive rocks, are here concentrated in the subordinate strata.

Turning westward we reached at length the ravine of gold (Quebrada del Oro). On examining the slope of a hill, we could hardly recognize the vestige of a vein of quartz. The falling of the earth caused by the rains had changed the surface of the ground, and rendered it impossible to make any observation. Great trees were growing in the places where the gold-washers had worked twenty years before. It is probable that the mica-slate contains here, as near Goldcronach in Franconia, and in Salzburgh, auriferous veins; but how is it possible to judge whether they be worth the expense of being wrought, or whether the ore is only in nodules, and in the less abundance in proportion as it is rich? We made a long herborization in a thick forest, extending beyond the Hato, and abounding in cedrelas, browneas, and fig-trees with nymphaea leaves. The trunks of these last are covered with very odoriferous plants of vanilla, which in general flower only in the month of April. We were here again struck with those ligneous excrescences, which in the form of ridges, or ribs, augment to the height of twenty feet above the ground, the thickness of the trunk of the fig-trees of America. I found trees twenty-two feet and a half in diameter near the roots. These ligneous ridges sometimes separate from the trunk at a height of eight feet, and are transformed into cylindrical roots two feet thick. The tree looks as if it were supported by buttresses. This scaffolding however does not penetrate very deep into the earth. The lateral roots wind at the surface of the ground, and if at twenty feet distance from the trunk they are cut with a hatchet, we see gushing out the milky juice of the fig-tree, which, when deprived of the vital influence of the organs of the tree, is altered and coagulates. What a wonderful combination of cells and vessels exist in these vegetable masses, in these gigantic trees of the torrid zone, which without interruption, perhaps during the space of a thousand years, prepare nutritious fluids, raise them to the height of one hundred and eighty feet, convey them down again to the ground, and conceal, beneath a rough and hard bark, under inanimate layers of ligneous matter, all the movements of organic life!

I availed myself of the clearness of the nights, to observe at the plantation of Tuy two emersions of the first and third satellites of Jupiter. These two observations gave, according to the tables of Delambre, longitude 4 hours 39 minutes 14 seconds; and by the chronometer I found 4 hours 39 minutes 10 seconds. During my stay in the valleys of the Tuy and Aragua the zodiacal light appeared almost every night with extraordinary brilliancy. I had perceived it for the first time between the tropics at Caracas, on the 18th of January, after seven in the evening. The point of the pyramid was at the height of 53 degrees. The light totally disappeared at 9 hours 35 minutes (apparent time), nearly 3 hours 50 minutes after sunset, without any diminution in the serenity of the sky. La Caille, in his voyage to Rio Janeiro and the Cape, was struck with the beautiful appearance displayed by the zodiacal light within the tropics, not so much on account of its less inclined position, as of the greater transparency of the air.* (* The great serenity of the air caused this phenomenon to be remarked, in 1668, in the arid plains of Persia.) It may appear singular, that Childrey and Dominic Cassini, navigators who were well acquainted with the seas of the two Indies, did not at a much earlier period direct the attention of scientific Europe to this light, and its regular form and progress. Until the middle of the eighteenth century mariners were little interested by anything not having immediate relation to the course of a ship, and the demands of navigation.

However brilliant the zodiacal light in the dry valley of Tuy, I have observed it more beautiful still at the back of the Cordilleras of Mexico, on the banks of the lake of Tezcuco, eleven hundred and sixty toises above the surface of the ocean. In the month of January, 1804, the light rose sometimes to more than 60 degrees above the horizon. The Milky Way appeared to grow pale compared with the brilliancy of the zodiacal light; and if small, bluish, scattered clouds were accumulated toward the west, it seemed as if the moon were about to rise.

I must here relate another very singular fact. On the 18th of January, and the 15th of February, 1800, the intensity of the zodiacal light changed in a very perceptible manner, at intervals of two or three minutes. Sometimes it was very faint, at others it surpassed the brilliancy of the Milky Way in Sagittarius. The changes took place in the whole pyramid, especially toward the interior, far from the edges. During these variations of the zodiacal light, the hygrometer indicated considerable dryness. The stars of the fourth and fifth magnitude appeared constantly to the naked eye with the same degree of light. No stream of vapour was visible: nothing seemed to alter the transparency of the atmosphere. In other years I saw the zodiacal light augment in the southern hemisphere half an hour before its disappearance. Cassini admitted "that the zodiacal light was feebler in certain years, and then returned to its former brilliancy." He thought that these slow changes were connected with "the same emanations which render the appearance of spots and faculae periodical on the solar disk." But this excellent observer does not mention those changes of intensity in the zodiacal light which I have several times remarked within the tropics, in the space of a few minutes.

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