160 Professor Denison Olmsted on the 



(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 orbits 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. There- 

 fore, the fluid which reflects to us the zodiacal light, is not 

 the atmosphere of the sun, and since it surrounds that body, 

 it must revolve about it according 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 

 composed, presents many analogies to that of comets. In 

 its visible form, in its direction with respect to the sun, in 

 its very shade and colour, in its increasing density towards 

 the sun, in its transparency 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 recognise a great resemblance 

 between the zodiacal light and the tails of comets. We are, 

 at least, authorised to say that it is a " nebulous body." 



From all the foregoing considerations on the nature and 

 constitution of the zodiacal light, we infer, then, that it is a 

 nebulous body, revolving around the sun in an orbit but 

 slightly inclined to the ecliptic. 



I proposed finally to inquire, whether or not the zodiacal 

 light is the origin of the meteoric shorvers of November and 

 August, and especially those of November. 



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

 meteoric shower of November 13, 1833, I published in the 

 American Journal of Science some observations on the phe- 

 nomena and causes of that remarkable exhibition of shooting 

 stars, in which I came to the conclusion that they 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 the earth passes on the 13th of Novem- 



