Zodiacal Light. 153 



lies far in the south-west, crosses the milky way, the head of 

 Capricornus, and has its vertex near the right shoulder of 

 Aquarius, with an elongation from the sun of full 90"". From 

 this time it climbs rapidly upwards, until by December 2, it 

 reaches nearly to Algenib in the equinoctial colure, having 

 an elongation of more than 100°. By about Christmas the 

 vertex reaches almost to Alpha Arietis, having an elonga- 

 tion of towards 120°. It becomes nearly stationary through 

 the month of January, but in February and March it moves 

 slowly onward through Taurus to Gemini, beyond which it 

 scarcely advances. The accompanying diagram (PI. II.) is 

 intended to represent the general appearance of the zodiacal 

 light, when seen under favourable circumstances. Near the 

 time of the vernal equinox, it is seen of a pyramidal form, 

 with a broad base resting on the horizon. Its northern bor- 

 der grazes the bright star Algenib in Pegasus, passes south 

 of Alpha Arietis seven or eight degrees, and about two de- 

 grees south of the Pleiades. Along its southern boundary 

 we recognize the stars in the mouth and neck of the Whale, 

 and still higher, Aldebaran, the Hyades, and the horns of 

 the Bull. The successive positions attributed to the zodiacal 

 light, from the time of its earliest appearance in the western 

 sky, the 21st of November, to the vernal equinox, are not abso- 

 lutely uniform, but they still correspond to observations made 

 during the six years before-mentioned, as will appear from a 

 few extracts from my record book. I have already recited 

 the observation of November 21, 1837, when the return of 

 the body to the western sky was first recognized. 



" Nov. 26, 1837. — Light feeble, Venus being very bright ; 

 but seen after Venus was set, reaching nearly to the Fish, 

 south of Pegasus. Elongation 100°. 



" Dec. 2. — New moon begins to interfere with observations, 

 but this evening the zodiacal light was visible after the moon 

 was set ; covers the Pentagon in Pisces, and reaches beyond 

 it. Elongation 1 10°. 



*' Dec. 18. — Early part of the day a violent rain and high 

 wind ; cleared off towards night ; zodiacal light very bright, 

 reaching at least to Alpha Arietis ; nearly as bright as the 

 milky way. Elongation 120°." 



