82 



THOUGHTS ON THE INFLUENCE OP ETHER 



time that the sun might dart matter in the plane of its equator, as far as the orbit of 

 Venus ; and that the light reflected from this matter was the cause of the phenomenon. 



He suspected, too, that there was a sympathy hctween the appearance of spots upon 

 the sun's surface and the changes in the zodiacal light * 



Euler was of opinion that the matter which produced the zodiacal light did not extend 

 to the sun, but surrounded it at a certain distance, in the form of a ring.f He is also the 

 author of an essay in the Memoires of the Academy of Berlin,^ in which the phenomenon 

 is ascribed to the prodigious extension of the sun's atmosphere in the equatorial region; 

 this extension being caused by the impulsion of the solar rays. 



M. Arago remarks, it is really strange that so decided a partisan of the undulatory 

 theory of light, so ardent an opponent of the Newtonian doctrine of emission, should give 

 so active a role to the impellent power of the sun's rays.§ 



The ring hypothesis has been adopted by Schubert, Boisson, and Humboldt; the last 

 considers that the ring is much compressed, and lies between the orbits of Venus and 

 Mars. 1 1 



Olbers believed that the matter composing the zodiacal light extends all the way to the 

 sun, and that the light seen round that body during a total eclipse, is caused by the por- 

 tion of the matter in that vicinity.fl 



These views of Olbers are entirely consistent with the conditions I have been endeavor- 

 ing to establish; they would have been more interesting, had he advanced some theory to 

 sustain the matter of the zodiacal light in the position which he supposed it to occupy. 



La Place entertained views upon the subject of the zodiacal light which were a part of 

 his grand scheme known as the Nebular hypothesis. He believed that after the denser 

 parts of the nebula had been consolidated into the sun and planets, there remained a sub- 

 tile portion, whose atoms revolved round the sun with velocities proportioned to their 

 distances.** 



Dr. Young supposed that the phenomenon was caused by the refraction of the sun's 

 light in the earth's atmosphere. But M. Arago asks, why, if this be the cause, should 

 the light be oblique to the horizon. 



One of the most modern hypotheses upon this subject, is that of our countryman, the 

 late Professor Olmstcad, of Yale College. He conceived that a nebulous body revolves 

 round the sun in an orbit of considerable excentricity, and in a period of six months. 

 The aphelion distance of the nebula he supposed to be equal to the radius of the earth's 

 orbit. On the 13th November he believed the earth and the nebula to pass that point, 



* Astronomie Populaire, vol. ii, p. 188. 

 § Astronomie Populaire, vol. ii, p. 190. 

 ** Astronomic Populaire, vol. ii, p. 191. 



f Op. citat., vol. ii, p. 188. 

 || Cosmos, vol. i, p. 141. 



:|: Vol. ii, 1748. 



Tf lb., vol. i, p. 14:j. 



