The Wind Having Freshened A Little Towards The Morning On The 18th, We Succeeded In Passing The Channel.

We drew very near the Infierno the second time, and remarked the large crevices, through which the gaseous fluids probably issued, when this basaltic mass was raised. We lost sight of the small islands of Alegranza, Montana Clara, and Graciosa, which appear never to have been inhabited by the Guanches.

They are now visited only for the purpose of gathering archil, which production is, however, less sought after, since so many other lichens of the north of Europe have been found to yield materials proper for dyeing. Montana Clara is noted for its beautiful canary-birds. The note of these birds varies with their flocks, like that of our chaffinches, which often differs in two neighbouring districts. Montana Clara yields pasture for goats, a fact which proves that the interior of this islet is less arid than its coasts. The name of Alegranza is synonymous with the Joyous, (La Joyeuse,) which denomination it received from the first conquerors of the Canary Islands, the two Norman barons, Jean de Bethencourt and Gadifer de Salle. This was the first point on which they landed. After remaining several days at Graciosa, a small part of which we examined, they conceived the project of taking possession of the neighbouring island of Lancerota, where they were welcomed by Guadarfia, sovereign of the Guanches, with the same hospitality that Cortez found in the palace of Montezuma. The shepherd king, who had no other riches than his goats, became the victim of base treachery, like the sultan of Mexico.

We sailed along the coasts of Lancerota, of the island of Lobos, and of Forteventura. The second of these islands seems to have anciently formed part of the two others. This geological hypothesis was started in the seventeenth century by the Franciscan, Juan Galindo. That writer supposed that king Juba had named six Canary Islands only, because, in his time, three among them were contiguous. Without admitting the probability of this hypothesis, some learned geographers have imagined they recognized, in the two islands Nivaria and Ombrios, the Canaria and Capraria of the ancients.

The haziness of the horizon prevented us, during the whole of our passage from Lancerota to Teneriffe, from discovering the summit of the peak of Teyde. If the height of this volcano is 1905 toises, as the last trigonometrical measure of Borda indicates, its summit ought to be visible at a distance of 43 leagues, supposing the eye on a level with the ocean, and a refraction equal to 0.079 of distance. It has been doubted whether the peak has ever been seen from the channel which separates Lancerota from Forteventura, and which is distant from the volcano, according to the chart of Varela, 2 degrees 29 minutes, or nearly 50 leagues. This phenomenon appears nevertheless to have been verified by several officers of the Spanish navy. I had in my hand, on board the Pizarro, a journal, in which it was noted, that the peak of Teneriffe had been seen at 135 miles distance, near the southern cape of Lancerota, called Pichiguera. Its summit was discovered under an angle considerable enough to lead the observer, Don Manual Baruti, to conclude that the volcano might have been visible at nine miles farther. It was in September, towards evening, and in very damp weather. Reckoning fifteen feet for the elevation of the eye, I find, that to render an account of this phenomenon, we must suppose a refraction equal to 0.158 of the arch, which is not very extraordinary for the temperate zone. According to the observations of General Roy, the refractions vary in England from one-twentieth to one-third; and if it be true that they reach these extreme limits on the coast of Africa, (which I much doubt,) the peak, in certain circumstances, may be seen on the deck of a vessel as far off as 61 leagues.

Navigators who have much frequented these latitudes, and who can reflect on the physical causes of the phenomena, are surprised that the peaks of Teyde and of the Azores* (* The height of this peak of the Azores, according to Fleurieu, is 1100 toises; to Ferrer, 1238 toises; and to Tofino, 1260 toises: but these measures are only approximative estimates. The captain of the Pizarro, Don Manuel Cagigal, proved to me, by his journal, that he observed the peak of the Azores at the distance of 37 leagues, when he was sure of his latitude within two minutes. The volcano was seen at 4 degrees south-east, so that the error in longitude must have an almost imperceptible influence in the estimation of the distance. Nevertheless, the angle which the peak of the Azores subtended was so great, that the captain of the Pizarro was of opinion this volcano must be visible at more than 40 or 42 leagues. The distance of 37 leagues supposes an elevation of 1431 toises.) are sometimes visible at a very great distance, though at other times they are not seen when the distance is much less, and the sky appears serene and the horizon free from fogs. These circumstances are the more worthy of attention because vessels returning to Europe, sometimes wait impatiently for a sight of these mountains, to rectify their longitude; and think themselves much farther off than they really are, when in fine weather these peaks are not perceptible at distances where the angles subtended must be very considerable. The constitution of the atmosphere has a great influence on the visibility of distant objects. It may be admitted, that in general the peak of Teneriffe is seldom seen at a great distance, in the warm and dry months of July and August; and that, on the contrary, it is seen at very extraordinary distances in the months of January and February, when the sky is slightly clouded, and immediately after a heavy rain, or a few hours before it falls.

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