TIIE APPARENT POSITION OF THE ZODIACAL LIGHT. ] -~)3 



tudes in the quadrant from 130° to 220° would be enhanced by the deficiency of 



perihelia, even when viewed from the Sun. To a terrestrial observer, the effect 

 would be still farther increased by the result of parallax, when the region observed 

 was in opposition. The coincidence of this theoretical result with that derived 

 from the observations of " Gegenschein " is not for the pn ent to be regarded as 



anything more than a suggestion, which may lend additional interest to future ob- 

 servations of light in the zodiac, and also to the discovery of more small planets, 

 which is often regarded as leading to no result of consequence. 



The six asteroids having southern perihelia, and ascending nodes between the 



longitudes 220° and 310°, are Hygiea (10), Pomona (32), Aethra (132), Pokna (142), 

 Xanthippe (156), and Loreley (165). The orbit of Aethra has a large inclination 



and eccentricity; those of the five others are not distinguished by any peculiarity 

 except that of the position of their nodes. The approximate longitudes of the 

 ascending nodes of these planets are respectively 286°, 221°, 260°, 292°, 246°, and 



304°; the corresponding values of the angles in the planes of their orbits by the 

 amounts of which their perihelia follow their ascending nodes are 311°, 333°, 253°, 



289°, 270°, and 333°. 



Upon the hypothesis that a noticeable amount of light is reflected to us by 

 meteors not more than two or three times farther from the Sun than we are, 

 this light would vary its position in longitude according to its elongation. At its 

 eastern elongation it would precede its heliocentric longitude, which it would fol- 

 low at its western elongation. Applying these considerations to the case of the 

 evening and morning zodiacal light, we see that if the light would tend to south 

 latitude at the longitude 0° as seen from the Sun, then, as seen from the Earth, 

 and at the elongation 60°, the evening zodiacal light should be farthest to the 



a " "~ o 



south at the longitude 340° or still sooner, while the morning light should have 

 its greatest southern latitude at 20° or later. A similar effect of parallax might 

 be expected at the maximum of north latitude. A reference to Table II. will 

 show that indications of these effects are in fact presented by the observations of 

 Jones. The coincidence is worth attention, although the uncertainty of the cor- 

 rection for atmospheric absorption employed in Table II. makes it difficult to 

 obtain more than a general conclusion from the corrected latitudes. 



It has been shown that the symmetrical part of the variation noticed above 

 in the number of ascending nodes at different longitudes may perhaps be due to 

 the circumstances under which asteroids have been discovered. But if we suppose 

 it to indicate a general tendency of such bodies, the band which they would form 



vol. XI 



20 



