152 Professor Denison Olmsted on the 



until the end of November it appears nearly stationary, 

 ascending from the horizon to the constellation Leo, in some 

 part of which it terminates, the vertex varying somewhat in 

 altitude with the condition of the sky. After the 13th of 

 November the light fades in the morning sky, contracts in 

 dimensions, and soon becomes stationary and then retrograde 

 with respect to the sun, proceeding eastward no farther than 

 y Virginis, a point which it reaches by the 26th of November, 

 having at this time an elongation of only 60°, whereas a 

 fortnight before the elongation was 90°. As the sun advances 

 in the ecliptic, while the light appears nearly stationary, the 

 elongation on this side continues to diminish, as well as the 

 dimensions and the illumination, until early in January, after 

 which it is scarcely seen in the east until August. 



The foregoing general statements are supported by obser- 

 vations taken at different times through the period of six 

 years before mentioned, a few of which I extract from my 

 records : — 



''Nov. 26, 1837. — This morning about daybreak saw the zo- 

 diacal light ; very bright and distinct, but elongation only 60°. 



" Nov. 28. — Commenced observations at 5 o'clock ; zodiacal 

 light brighter than usual in preceding years at this season, 

 but the vertex appears nearly stationary in Gamma Virginis. 



" Dec. 5. — Zodiacal light visible this morning as early as 

 3 o'clock ; not quite so bright as on the 28th of November, 

 but increased in brightness from 3 o'clock till daybreak ; 

 vertex still in y Virginis. 



*' Dec. 9. — Examined the eastern sky from 4^ 30"^ till day- 

 break ; very cold and clear ; zodiacal light much less bright 

 than on the 5th ; width also less ; when I first went out could 

 scarcely see it ; became distinct by 5 o'clock, half an hour 

 before daybreak, yet much feebler than it was ten days ago ; 

 contracted between Spica and Theta Virginis, 4° north of 

 Spica, whereas a few days since the border grazed this star. 



" Jan. 18, 1837. — Zodiacal light very dift'usive and ill-de- 

 fined ; seen after this no more in the east.'' 



We will now introduce the observer to the western sky. 

 Here the zodiacal light first comes into view, so as to be dis- 

 tinctly defined, about the 21st of November, at which time it 



