IN THE SOLAR SYSTEM. 



81 



justifies the description already given to it, viz., a huge plate, whose sides incline a little 

 from the plane of the sun's equator, so as to give it the character of a hollow cone ; the 

 sun's centre occupying the apex of the cone. 



Now, how should such a figure appear to an inhabitant of our planet"? The earth can 

 never be much removed from the plane of the sun's equator, nor from the body of this 

 mass of heated ether. The mass being seen very obliquely, should have the appearance 

 of a great spindle, whose long axis lies a little north of the plane of the sun's equator. 

 If the current of ether carry reflecting matter as far as, or beyond the orbit of the earth, 

 the spindle should extend 90° or more from the sun. 



As the earth's orbit is most distant from the plane of the sun's equator, at the points 

 passed by the planet in March and September, the spindle should, at those seasons, have 

 the greatest breadth. More particularly in March, because the earth is then to the south, 

 and the mass to the north of the plane of the sun's equator. While in September the 

 mass is between the earth and the plane of the sun's equator* 



It is not possible to allow our thoughts to pursue this train, without finding that our 

 minds rest upon the Zodiacal light as the evidence of the truth of our reflections. 



The zodiacal light in our latitude is seen after sunset in the months of March, April, 

 and May, and before ..sunrise during the opposite season of the year. It extends along 

 the zodiac, and accompanies the sun in its annual course through the heavens. 



It has the form of an ellipse or elongated spindle. The dimensions of the light are 

 variable, its long axis, which coincides nearly with the plane of the sun's equator, extend- 

 ing, according to different observers, from forty to one hundred degrees from the sun. The 

 breadth of its base varies from eight to thirty degrees. It does not efface the light of the 

 smallest stars. 



Cassinij one of the earliest observers of the phenomenon, thought the mass of light was 

 not divided equally by the ecliptic; the greater portion being to the north of that great 

 circle. This fact lias been confirmed by the observations of Fatio de Duillier, made at 

 Geneva, in 1085 and 1686.f 



From observations made at Paris and Geneva, it is established that the zodiacal light 

 has not always the same intensity ; it varies from year to year, and even within the limits 

 of a few days. 



Among the speculations into the cause of the zodiacal light by the astronomers of the 

 seventeenth and eighteenth centuries, we find very discordant views entertained by the 

 same individuals. 



J. I). Cassini conceived that the zodiacal light was a nebulous ring surrounding the sun. 

 He believed that the ring contained small planetary bodies.j lie admitted at another 



* See Fig. 6. 



VOL. XIII. — 11 



| Astronomie Populaire, vol. ii, p. 18C. 



J Cosmos, vol, i, p. HI- 



