34 SANTA CRTIZ. 



points out a limit beyond which the latter are more 

 distinctly detached from the azure vault of the sky. 



The aerial light projected on the tops of hills in- 

 creases the visibility of those which are seen posi- 

 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 exceed- 

 ing 121 miles ; but experience goes against this con- 

 clusion. The Peak of Teneriffe has often been ob- 

 served 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 in- 

 visible. After repeatedly sounding, on account of the 

 thickness of the mist, they anchored in the road of 

 Santa Cruz, when at the moment they began to salute 

 the place the fog instantaneously dispersed, 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 ves- 

 sel 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 observations 

 for determining the longitude of the mole of Santa 

 Cruz and the dip of the needle. Berthoud's chro- 



