164 Professor Denison Olmsted on the Zodiacal Light. 



1. The zodiacal light, as we have found in our inquiry into 

 its nature and constitution, is a nebulous body. 



2. It has a revolution around the sun. 



3. It reaches beyond and lies over the eartKs orbit at the 

 time of the November meteors, and makes but a small angle 

 with the ecliptic. 



4. Like the " nebulous body," its periodic time is comynen- 

 surable with that of the earth, so as to perform a certain whole 

 number of revolutions while the earth performs one, and thus 

 to complete the cycle in one year, at the end of which the 

 zodiacal light and the earth return to the same relative po- 

 sition in space. This necessarily follows from the fact, that 

 at the same season of the year it occupies the same position 

 one year with another, and the same now as when Cassini 

 made his observations nearly 170 years ago.* 



5. In the meteoric showers of November, the meteors are 

 actually seen to come from the extreme portions of the zodiacal 

 light, or rather a little beyond the visible portions ; and the 

 same was true of the radiant point of the meteors (when 

 watched as it was by Mr Fitch, t from October 16 to Novem- 

 ber 13, 1837), namely, that the radiant always keeps the same 

 relative position with respect to the vertex of the zodiacal 

 light, being with that vertex in Gemini, in the month of Oc- 

 tober, and travelling along with it through the constellation 

 Cancer, and into Leo, where it was on the morning of the 

 meteoric shower. Observations, so far as they have been 

 made, indicate a similar relation between the meteors of 

 August and the extreme portions of the zodiacal light. 



These five propositions I offer as so many facts established 

 by observation. Most of them appear in the original paper 

 of Cassini on the zodiacal light ; others may be seen in the 

 tabular collection by Houzeau of all the known observations 

 made at different periods ; a few, not noted by others, have 

 been added by myself. For the inferences here made re- 

 specting the connection of this body with the periodical me- 

 teors, I alone am responsible. 



* For the first suggestion of this analogy, I am indebted to one of my former 

 pupils, Mr Hubert Newton. 



t Amer. Jpiir. Sci., xxxiii., 38G. 



