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ceased long before daylight had rendered the 

 stars quite invisible. I have faithfully related 

 what we saw during the twilight, without under- 

 taking to explain this extraordinary phenome- 

 non, of which I published an account in Baron 

 Zach's Astronomical Journal, twelve years ago. 

 The motion of the vesicular vapours, caused by 

 the rising of the sun ; the mingling of several 

 layers of air, the temperature and density of 

 which were very different, no doubt contributed 

 to produce an apparent movement of the stars 

 in the horizontal direction. We see something 

 similar in the strong undulations of the solar 

 disk, when it cuts the horizon ; but these un- 

 dulations seldom exceed twenty seconds, while 

 the lateral motion of the stars, observed at the 

 Peak, at more than 1800 toises, was easily dis- 

 tinguished by the sight alone, and seemed to 

 exceed all that we have thought it possible to 

 consider hitherto as the effect of the refraction 

 of the light of the stars. On the top of the 

 Andes, at Antisana, I was present at sunrise, 

 and passed the whole night at 2100 toises, with- 

 out noting any appearance resembling this phe- 

 nomenon. 



I was anxious to make an exact observation 

 of the instant of sunrising at an elevation so con- 

 siderable as that we had reached on the Peak of 

 TenerifFe. No traveller, furnished with instru- 

 ments, had as yet taken such an observation. I 



vol. i. m 



