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Prof. Olmsted on the Zodiacal Light. 313 



February and March it moves slowly onward through Taurus to 

 Gemini, beyond which it scarcely advances. The accompanying 

 diagram (PL 11,) is intended to represent the general appearance oi 

 the zodiacal light, when seen under favorable circumstances near 

 the time of the vernal equinox. It is seen of a pyrann'dal form with 

 a broad base resting on the horizon. Its northern border grazes 

 the bright star Algenib in Pegasus, passes south of Alpha Arietis 

 seven or eight degrees, and about two degrees south of the Pleia- 

 des. Along its southern boundary we recognize the stars in the 

 mouth and neck of the Whale, and still higher, Aldebaran, the 

 HyadeSj and the horns of the Bull. The successive positions 

 attributed to the zodiacal light from the time of its earliest ap- 

 pearance in the western sky, the 2 1st of November, to the ver- 

 nal equinox, are not absohitely uniform, but they siill correspond 

 to observations made during the six years before mentioned, as 

 will appear from a few extracts from my record book. 1 have 

 already recited the observation of November 21st, 1837, when 

 the return of the body to the western sky was first recognized, 



JVbi\ 26, 1837. — Light feeble, Venus being very bright; but seen 

 after Venus was set, reaching nearly to the Fish south of Pegasus. 

 Elongation 100°. 



Bee. 2, — New moon begins to interfere with observations; but this 

 evening ihe zodiacal light was visible after the moon was set- Covers 

 the Pentagon in Pisces and reaches beyond it. Elongation llO"". 



Bee, 18, — Early part of the day a violent rain and high wind. 

 Cleared off towards night. Zodiacal hght very bright, reaching at least to 

 Alpha Arietis — nearly as bright as the milky way. Elongauon 120''. 



It ought to be remarked that the phemonena of this^body 

 Were peculiarly striking in the autumu and winter of ISST, and 

 the observations made this year show a greater intensity of 

 light and a greater elongation from the sun than tliose of corres- 

 ponding dates in 1835 and 1836. 



Dec. 21, 1835. — This evening atmosphere very transparent. Zo- 

 diacal light very conspicuous, reaching nearly to Algenib, though quite 

 faint towards the vertex. Elongation 90°. 



Dec. 28, 1837.— Night favorable. Appeared to me not to reach 

 quite so far eastward as it did a few nights since — certainly not beyond 

 the equinoctial colure. Could not be certain much further than the 

 pentagon of stars in Pisces. Elongation 75°. 



February 7. — Zodiacal light very conspicuous since the last moon, 

 but has advanced eastward "very little since Christmas, still reaching 

 only to Alpha Arietis. Elongation 75°. 



Feb. 24.— First night since the moon has been away. Sky favorable 

 for observation. Zodiacal light bright and well defined, its axis nearly 

 in the ecliptic. Reaches to the space between Aldebaran and the Plei- 

 ades. Elongation 85°. 



March 26.— Zodiacal light very bright, reaching above the Pleiades, 

 which are a little north of the axis. Elongation 60°. 



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