UNDULATION OP THE STARS. 5 



cars near the horizon flickering with a singular oscillating 

 motion. Luminous points ascended, moved laterally, and 

 feii back to their former position. This phenomenon lasted 

 only from seven to eight minutes, and ceased long before the 

 sun's disk appeared above the horizon of the sea. The same 

 .motion was discernible through a telescope, and there was 

 no doubt that it was the stars themselves which moved.* 

 Did this change of position depend on the much-contested 

 phenomenon of lateral radiation ? Does the undulation of 

 the rising sun's disk, however inconsiderable it may appear 

 when measured, present any analogy to this phenomenon in 

 the lateral alteration of the sun's margin ? Independently 

 of such a consideration, this motion seems greater near the 

 horizon. This phenomenon of the undulation of the stars 

 was observed almost half a century later at the same spot 

 by a well-informed and observing traveler, Prince Adalbert 

 of Prussia, who saw it both with the naked eye and through 

 a telescope. I found the observation recorded in the prince's 

 manuscript journal, where he had noted it down, before he 

 learned, on his return from the Amazon, that I had wit- 

 nessed a precisely similar phenomenon.! I was never able 

 to detect any trace of lateral refraction on the declivities 

 of the Andes, or during the frequent mirages in the torrid 

 plains or Llanos of South America, notwithstanding the het- 

 erogeneous mixture of unequally-heated atmospheric strata. 

 As the Peak of Tenerifie is so near us, and is so frequently 



* Humboldt, in Fr. von Zach's Monatliche Correspondenz zur Erd- 

 und Himmels-Kunde, bd. i., 1800, s. 396 ; also Voy. aux R6g. Equin., 

 torn, i., p. 125 : " On croyait voir de petites fusses lancees dans 1'air. 

 Des points lumineux eleves de 7 a 8 degres, paraissent d'abord se mou- 

 voir dans le sens vertical, mais puis se convertir en une veritable oscil- 

 lation horizontale. Ces images lumineux etaient des images de plu- 

 sieurs etoiles agrandies (en apparence) par des vapeurs et revenant au 

 meme point d'ou elles etaient partis." " It seemed as if a number of 

 sinall rockets were being projected in the air ; luminous points, at an 

 elevation of 7 or 8, appeared moving, first in a vertical, and then os- 

 cillating iu a horizontal direction. These were the images of many 

 stars, apparently magnified by vapors, and returning to the same point 

 from which they had emanated." 



t Prince Adalbert of Prussia, Aus meinem Tagebuche, 1847, s. 213. 

 Is the phenomenon I have described connected with the oscillations 

 of 10"-12", observed by Carlini, in the passage of the polar star over 

 the field of the great Milan meridian telescope ? (See Zach's Corres- 



endance Astronomique et Giog., vol. ii., 1819, p. 81.) Brandes (Geh- 

 's Umgearb. Phys. Wortersb., bd. iv., s. 549) refers the phenomenon 

 to mirage. The star-like heliotrope light has also frequently been seen, 

 by the admirable and skillful observer, Colonel Baeyer, to oscillate to 

 and fro in a horizontal direction. 



