46 A GRAND ILLUMINATION. 



were like rocks amidst tliis vast sea of vapours, and their 

 black tints were in fine contrast with the whiteness of 

 the clouds. 



While thej wiere climbing over the broken lavas of 

 the Malpays, they perceived a very curious optical phe- 

 nomenon, which lasted some minutes. They thought 

 they saw on the east side small rockets thrown into the 

 air. Luminous points, about seven or eight degrees 

 above the horizon, appeared first to move in a vertical 

 direction -^ but their motion was gradually changed into 

 a horizontal oscillation. Their fellow-travellers, their 

 guides even, were astonished at this phenomenon, with- 

 out either Humboldt or Bonpland having made any 

 remark on it to them. The travellers thought, at first 

 sight, that these luminous points, which floated in the 

 air, indicated some new eruption of the great volcano of 

 Lancerota; for they recollected that Bouguer and La 

 Condamine, in scaling the volcano of Pichincha, were 

 witnesses of the eruption of Cotopaxi. But the illusion 

 soon ceased, and they found that the luminous points 

 were the images of several stars magnified by the vapours. 

 These images remained motionless at intervals, they then 

 seemed to rise perpendicularly, descended sideways, and 

 returned to the point whence they had departed. This 

 motion lasted one or two seconds. Though they had no 

 exact means of measuring the extent of the lateral shift- 

 ing, they did not the less distinctly observe the path of 

 the luminous point. It did not appear double from an 

 efiect of mirage, and left no trace of light behind. 

 Bringing, with the telescope of a small sextant, the stars 

 into contact with the lofty summit of a mountain in 

 Lancerota, Humboldt observed that the oscillation was 



