97 



to grow paler compared with the brilliancy of 

 the zodiacal light ; and if small, bluish, scat- 

 tered clouds were accumulated toward the 

 West, it seemed as if the Moon were going to 

 rise. 



I must here relate another very singular fact, 

 which is several times noted in my private 

 journal written on the spot. On the 18th of 

 January, and the 15th of February, 1800^ the 

 intensity of the zodiacal light changed in a very 

 perceptible manner, at intervals of two or three 

 minutes. Sometimes it was very faint, at others 

 it surpassed the brilliancy of the Milky Way in 

 Sagittarius. The changes took place in the 

 whole pyramid, especially toward the interior, 

 far from the edges. During these variations of 

 the zodiacal light, the hygrometer indicated a 

 considerable dryness. The stars of the fourth 

 and fifth magnitude appeared constantly to the 

 naked eye with the same degree of light. No 

 stream of vapour was visible, nothing seemed to 

 alter the transparency of the atmosphere. In 

 other years I saw the zodiacal light augment in 

 the southern hemisphere half an hour before it's 

 disappearance. Dominic Cassini admitted * 9 

 " that the zodiacal light was feebler in certain 

 years, and then returned to it's former bril- 

 liancy." He thought, that these slow changes 



* Mem. de V Academic, vol. viii, p. 164 and 208. 

 VOL. IV. H 



