237 



rain, behind the castle of St. Antonio. As soon 

 as she appeared on the horizon, we distinguish- 

 ed two circles ; one large and whitish, forty- 

 four degrees in diameter ; the other a small cir- 

 cle of 1° 43', displaying all the colors of the 

 rainbow. The space between the two circles 

 was of the deepest azure. At four degrees 

 height, they disappeared, while the meteorolo- r 

 gical instruments indicated not the slighest 

 change in the lower regions of the air. This 

 phenomenon had nothing extraordinary, except 

 the great brilliancy of the colors, added to the 

 circumstance^ that, according to the measures 

 taken with Ramsden's sextant, the lunar disk 

 was not exactly in the centre of the haloes. 

 Without this actual measurement, we might 

 have thought, that the excentricity was the effect 

 of the projection of the circles on the apparent 

 concavity of the sky *. The form of the haloes, 



* The 17th of August, 1799: thermometer, 25° 3'; 

 Deluc's hygrometer, 68°. The altitude of the Moon being, 

 11° 8\ the horizontal diameter of the little corona was lo50', 

 and it's vertical diameter 1° 43'. The distance from the 

 centre of the Moon to the upper edge of the small halo was 

 forty-one minutes, and to the lower edge fifty-nine minutes. 

 The whole space between the lunar disk and the extremity of 

 the small halo shone with prismatic colors. The horizontal 

 diameter of the large white halo was 42° 3'. When the 

 Moon had attained the altitude of 37° 34' above the horizon, 

 the diameter of the greater halo was 44° 10', and the breadth 

 of the milky band 3° 35'. The Moon no longer showed any 



2 m 2 



