312 ProJ. Olmsted on the Zodiacal Light. 



25th of October, to occupy the space south of Denebola in the 

 tail of the Lion, terminating a little above Regulus. From this 

 time until the middle 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 

 Hght fades in the morning sky, contracts in dimensions, and soon 

 becomes stationary and then retrograde with respect to the sun, 

 proceeding eastward no further than 7 Virginis, a point which it 

 reaches by the 26th of November, having at this time an elonga- 

 tion of only 60^, whereas a fortnight before the elongation was 

 90^. As the sun advances in the ecliptic, while the light ap- 

 pears nearly stationary, the elongation on this side continues to 

 diminish, as well as the dimensions and the ilUunination, until 

 early in January, after which it is scarcely seen in the east until 

 August. 



The foregoing general statements are supported by observa- 

 tions taken at different times through the period of six years be- 

 fore mentioned, a few of which I extract from my records: 



iVbu. 26, 1S37. — This morning about daybreak, saw the zodiacal 

 light — very briglit and di.siinct, but elongation only 60°. 



Nov, 2H. — Commenced observau'ons at 5 o'clock. Zodiacal h'ght 

 brighter than usual in preceding years at this season, but the vertex 

 appears nearly slaiionary in Gamina Virginis. 



Dec, 5. — Zodiacal light visible this morning as early as 3 o'clock. 

 Not quite so bright as on the 28ih of November, but increased in 

 brightness from 3 o'clock till daybreak — vertex still in -/ Virginis. 



Dec. 9. — Examined the eastern sky from 4'' 30'» till "daybreak. 

 Very cold and clear. Zodiacal light much less bright than on the 5ih. 

 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 Vir- 

 ginis, 4° north of Spica, whereas a- few days since the border grazed 

 this star. 



Jan. IS, 1837, — Zodiacal light very diffusive and ill-defined. Seen 

 after this no more in the east. 



We will now introduce the observer to the western sky. Here 

 the zodiacal light first conies into view^ so as to be distinctly de- 

 fined, about the 21st of November, at which time it lies far in 

 the southwestj crosses the milky way, the head of Capricornns, 

 and has its vertex near the right shoulder of Aquarius, with an 

 elongation from the sun of full 90P. From this time it climbs 

 rapidly upwards, until by December 2d it reaches nearly to Al- 

 genib in the equinoctial colure, having an elongation of more 

 than 100^. By about Christmas the vertex reaches almost to 

 Alpha Arietis, having an elongation of towards 120^. It be- 

 comes nearly stationary through the month of January; but ia 



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