Zodiacal Light. 283 



Cassini, who observed it for about 8 days. It 

 has obtained the name of the zodiacal light, 

 because it appears along the zodiac in the form 

 of a lance or pyramid. It is of a faint whitish 

 colour resembling the milky way. 



The zodiacal light is more or less visible ac- 

 cording to circumstances. It is most apparent 

 when it has a sufficient extent along the zodiac, 

 and when the obliquity of the zodiac to the 

 horizon is not too great, for otherwise its faint 

 light will scarcely be distinguished from the 

 twilight, whether previous to the rising of the 

 sun, or after his setting. 



The zodiacal light appears generally in a 

 conical form, having its base always directed to- 

 wards the body of the sun, and its point towards 

 some star in the zodiac. It is thus it appears 

 in the evening in the spring, and in the morning 

 in the autumn. Its eastern point being dis- 

 played in the evening, and its western in the 

 morning. The two points may sometimes be 

 seen in the same night, as at the solstices, and 

 particularly at the winter solstice, when the 

 ecliptic makes, in the evening and the morning, 

 angles, almost equal with the horizon, and suf- 

 ficient to leave a considerable part of the point 

 above the line of twilight. The summer solstice 

 has the disadvantage of the too great obliquity 

 of the ecliptic with respect to the horizon and of 

 a long twilight. 



In the evening and morning observations, 



