160 I 



guides even, were astonished at this phenome- 

 non, without our having made any remark on 

 it to them. We thought at first sight, that these 

 luminous points, which floated in the air, indi- 

 cated some new eruption of the great volcano of 

 Lanzerota. We recollected, that Bouguer and 

 La Condamine, in scaling the volcano of Pichin- 

 cha, were witnesses of the eruption of Cotopaxi ; 

 but the illusion soon ceased, and we found, that 

 the luminous points were the images of several 

 stars magnified by the vapors. These images 

 remained motionless at intervals, they then 

 seemed to rise perpendicularly, descended side- 

 ways, and returned to the point whence they 

 had departed. This motion lasted one or two 

 seconds. Though we had no exact means of mea- 

 suring the greatness of the lateral shifting, we did 

 not less distinctly observe the path of theluminous 

 point. It did not appear double from an effect 

 of looming (mirage), and left no trace of light 

 behind. Bringing, with the telescope of a small 

 sextant by Troughton, the stars into contact 

 With the lofty summit of a mountain in Lanzero- 

 ta, I observed, that the oscillation was constantly 

 directed toward the same point, that is to say, 

 toward the part of the horizon where the disk 

 of the sun was to appear ; and that, making al- 

 lowance for the motion of the star in it's decli- 

 nation a the image returned always to the same 

 place. These appearances of lateral refraction 



