MAY BE SEEN AT SEA. 39 
tively, but diminishes that of such as are detached 
with a brown colour. Bouguer, proceeding on theo- 
retical data, has found that mountains which are 
seen negatively cannot be perceived at distances 
exceeding 121 miles; but experience goes against 
this conclusion. The Peak of Teneriffe has often been 
observed at the distance of 124, 131, and even 138 
miles; and the summit of Mowna-Roa in the Sand- 
wich Isles, which is probably 16,000 feet high, has 
been seen, at a period when it was destitute of snow, 
skirting the horizon from a distance of 183 miles. 
This is the most striking example yet known of the 
visibility of high land, and is the more remarkable 
that the object was negatively seen. 
The atmosphere continuing hazy, the navigators 
did not discover the island of Grand Canary, not- 
withstanding its height, until the evening of the 
18th June. On the following day they saw the point 
of Naga, but the Peak of Teneriffe still remained 
invisible. After repeatedly sounding, on account 
of the thickness of the mist, they anchored in the 
road of Santa Cruz, when at the moment they be- 
gan to salute the place the fog instantaneously dis- 
persed, and the Peak of Teyde, illuminated by the 
first rays of the sun, appeared in a break above the 
clouds. Our travellers betook themselves to the 
bow of the vessel to enjoy the majestic spectacle, 
when, at the very moment, four English ships were 
seen close astern. The anchor was immediately got 
up, and the Pizarro stood in as close as possible, to 
place herself under the protection of the fort. 
While waiting the governor’s permission to land, 
Humboldt employed the time in making observa- 
tions for determining the longitude of the mole of 
