Zodiacal Light. 156 



To present at one view the various elongations from the 

 sun, observed from Nov. 21 to May 10, the result is as fol- 

 lows : — 



1. Nov. 21. Elongation 90° 7. Feb. 7. Elongation 75° 



8. Mar. 29. „ 60 



9. April 6. Light rapidly 

 fading. 



10. May 1. Elongation 60 



11. May 10. „ 57 



From this tabular view, it appears that when the body first 

 came into view, on the 21st of November, it extended about 

 90° eastward of the sun ; that its elongation increased rapidly 

 from this period, being five days afterwards 100°, in six days 

 more 110°, and in sixteen days after this 120°, which is the 

 greatest elongation I have ever noticed ; and being at the 

 same time about 60° westward of the sun, its whole extent 

 in longitude was 180°. 



I have, in a few instances, remarked what was apparently 

 a sudden and remarkable expansion of the zodiacal light, a 

 circumstance more than once noted by Cassini. My record 

 for November 21, 1838, is as follows : — 



" At 5 A.M., about 20 minutes before twilight, the zodiacal 

 light was very large, extending in breadth from Corvus to 

 Arcturus. Never saw it so broad before. More inclined to- 

 wards the south than usual, its vertex passing one or two 

 degrees to the south of Regulus." 



Whether this extraordinary enlargement in breadth, im- 

 plying a space of more than 40°, was owing to a change in 

 the body itself, or to some unusual atmospheric refraction, 

 or the accidental presence of an aurora borealis, it is im- 

 possible for me to decide. 



It is well known that the great French astronomer, Do- 

 minique Cassini, was the first to direct the attention of astro- 

 nomers towards the zodiacal light, and that he made numerous 

 observations on it extending from 1683 to 1688 inclusive, 

 which are published in the eighth volume of the Memoirs of 

 the French Academy, together with observations on the 

 same phenomenon made at Geneva by a friend of his, M. 

 Fatio. An elaborate digest of these records is made by 



