318 Prof. Olmsted on the Zodiacal Light. 



At one time, as we have seen, its elongation from the sun in- 

 creases rapidly from 90^ to 120^; at other times it becomes for 

 considerable periods stationary among the stars, and even retro- 

 grade ; facts which seem to imply motions oi its own independ- 

 ent of the sun and the earth ; and such motions in any body 

 thus situated, though they might be greatly modified by per- 

 spective, can hardly be any other than motions of revolution. 

 On this subject La Place has the following remarks, at the end 

 of his chapter ^^on the figure of the atmosphere of the sun." 



(1.) " This atmosphere can extend no further than to the orbit 

 of a planet, whose periodical revolution is performed in the same 

 time as the sun's rotary motion about its axis, or in twenty-five 

 days and a half. Therefore, it does not extend so far as the or- 

 bits of Mercury and Venus, and we know that the zodiacal light 

 extends much beyond them. 



(2.) " The ratio of the polar to the equatorial diameter of the 

 solar atmosphere, cannot be less than two-thirds, and the zodiacal 

 light appears under the form of a very flat lens, the apex of which 

 is in the plane of the solar equator. Therefore, the fluid which 

 reflects to us the zodiacal light, is not the atmosphere of the sun, 

 and since it surrounds that bodv, it must revolve about it accord- 

 mg to the same laws as the planets : perhaps this is the reason 

 why its resistance to their motions is insensible." 



4. Material. — The matter of which the zodiacal light is com- 

 posed, presents many analogies to that of comets. In its visible 

 form, in its direction with respect to the sun, in its very shade 

 and color, in its increasing density towards the sun, in its trans- 

 parency which, as in comets, is such as to permit small stars to 

 be seen through almost every part of it; in all these respects we 



recognize a great resemblance between the zodiacal light and the 



tails of cornets. We are at least authorized to saj .__ 

 "nebulous body." 



From all the foregoing considerations on the nature and con- 

 stitution of the zodiacal light, we infer, then, that it is a nebu- 

 lous body, revolving around the sun in an orbit but slightly in- 

 clined to the ecliptic. 



I proposed finally to inquire whether or not the zodiacal light 

 is the origin of the meteoric shotvers of November and August, 

 and especially those of November. 



It may be known to some present that after the great meteoric 

 shower of November 13th, 1833, I published in the American 

 Journal of Science some observations on the phenomena and 

 causes of that remarkable exhibition of shooting stars, in which 

 I came to the conclusion that ihey proceeded from a nebulous 

 body revolving about the sun, and, at its aphelion, approaching 

 very near to that part of the earth's orbit through which tlie 

 earth passes on the 13th of November. At the conclusion of the 



