ASTRONOMY AND METEOROLOGY. 403 



with the sun for its centre, extending near to or beyond the earth's orbit. 

 Another hypothesis supposes that this nebulous ring has the earth for its cen- 

 tre ; and s-till others surmise that this phenomena is nebulous matter floating 

 in space, to which the periodical showers of stars may be traced, as the earth 

 happens in its orbit to pass through or encounter them. It seems impossible 

 to reconcile any of these hypotheses or surmises with the facts which close 

 observation has developed. They fail to satisfy us of their correctness, as 

 they arc soon perceived to be inconsistent with well ascertained facts. 



The zodiacal light, when first visible on a clear horizon, appears as a semi- 

 circular arc, with six or ten degrees base, well designed and distinct to the 

 eye, though no two persons could trace the same outline of it. As darkness 

 progresses, this semi-circular arc elongates upwards, in successive altitudes, 

 sometimes to the altitude of sixty degrees. When it has attained its highest 

 point, the diffused light becomes visible, extending on each side over a large 

 area, until lost in the obscurity of night. It is totally different from the ex- 

 tended light of sunset, with crepuscular rays, or the diffused light of twi- 

 light. When it becomes visible, it continues so, gradually lessening in 

 height, until the whole is lost beneath the horizon. Its apex is always ob- 

 served in the ecliptic, to the east or west of the sun, usually at the distance 

 of sixty to eighty degrees, but at times, under favorable circumstances, it is 

 seen to extend as far as 110 degrees. 



The evening and morning zodiacal light in the same latitude do not cor- 

 respond in phase or azimutn. This, though among the remarkable facts it 

 exhibits, has never been taken into consideration in any of the theories 

 hitherto advanced. Its peculiar phase and the constant change of azimuth 

 and inclination, whether the observer remains stationary for any time or 

 varies his position in latitude, should satisfy every one that it cannot be far 

 removed from the earth. Attentive and close observation shows that its va- 

 riations in azimuth correspond to the regular changes of the plane of the 

 ecliptic with the observer's horizon or with the vertical line passing through 

 his zenith. Its phases will be seen to be dependent upon the latitude. The 

 vividness of the light and its extent are in like manner to be ascribed to the 

 observer's position on the earth. Within the tropics, and when the ecliptic 

 is perpendicular to the horizon, the zodiacal light is confined to a slender 

 column having its diffused light widely extended. Without the tropics it is 

 always seen very much inclined to the horizon. It then assumes the ap- 

 pearance of a cone, cut more or less obliquely by the horizon. In northern 

 latitudes the light had a greater altitude than in more southern ones ; but 

 owing to the long twilights, was little visible, though it might be observed in 

 the vernal and autumnal equinoxes even in this latitude. The light in the 

 morning was not of the same color as in the evening ; in the first case being 

 grayish, in the other having a reddish blush, depending on the approach or 

 retreat of the sun. After sunrise, he had seen it reach the zenith, with a 

 breadth of only two and a half degrees. Sometimes the phenomenon was 

 very beautiful, as if a gauze veil were spread over the atmosphere, through 

 which the stars could be readily, though dimly seen. Thus the light stood 

 alone and distinct from, all others ; its central line being parallel to the eclip- 



