40 
TEAK OF TETDE. 
with the ocean, and a refraction equal to (H)79 of distance, 
It has been doubted whether the peak has ever been seen 
from the channel which separates Lancerota from Forte- 
ventura, and which is distant from the volcano, according to 
the chart of Varela, 2“ 29',' or nearly 50 leagues. This phe- 
nomenon 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 dis- 
tance, near the southern cape of Lancerota, called Pichi- 
gnera. Its summit was discovered under an angle consi- 
derable 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. Beckoning fifteen feet for the ele- 
vation oi the 63 0 , I find, that to render an account of this 
phenomenon, we must suppose a refraction equal to 0T5S of 
the arch, which is not very extraordinary for the temperate 
zone. According to the observations of General Bov, the 
refractions vary in England from one-twentieth to one-third; 
and if it bo true that they reach these extreme limits on 
the coast of Africa, (which I much doubt,) the peak, in cer- 
tain 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 pheno- 
mena, are surprised that the peaks of Tcyde and of the 
Azores* arc 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 
* The height of this peak of the Azores, according to Fleurien, is 1,100 
toises; to Ferrer, 1,238 toises; and to Tofino, ],2G0 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 ot .i 7 leagues, when he was sure of his 
latitude within two minutes. The volcano was seen at 4° S. E., 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 1,431 toises. 
