810 



/ 



grometer was at 57°. I had remained upon the 

 deck to observe the culmination of some great 

 stars. The full-moon was very high ; suddenly, 

 on the side of the orb, 45 ' before its passage 

 over the meridian, a great arc was formed 

 tinged with all the prismatic colours, but of a 

 gloomy aspect. The arch appeared higher than 

 the moon ; this iris-band was near 2° broad, and 

 its summit seemed to rise nearly from 80° to 85° 

 above the horizon of the sea. The sky was 

 singularly pure ; there was no appearance of 

 rain ; and what struck me most was, that this 

 phenomenon, altogether resembling a lunar 

 rainbow, was not opposite to the moon. The 

 arch remained stationary, or at least appeared 

 to do so, during eight or ten minutes, and at 

 the moment when I tried if it were possible to 

 see it by reflection in the mirror of the sextant, 

 it began to move and descend, crossing suc- 

 cessively the Moon and Jupiter, placed at a 

 small distance below the Moon. It was 12 h 54' 

 (real time) when the summit of the arch sank 

 below the horizon. This movement of 'a co- 

 loured arch filled with astonishment the mariners 

 who were upon their watch on the deck ; they 

 pretended, as they do on the appearance of every 

 extraordinary meteor, that " it announced 

 wind." M. Arago examined the sketch of this 

 arch in my journal, and thinks that the image 

 of the moon reflected in the waters would Hot 



