154 THE APPARENT POSITION OF THE ZODIACAL LIGHT. 



should be narrower near the longitudes 0° and 180° than near the longitudes 90° 

 and 270°. The column in Table II. giving half the extent of the zodiacal light 

 in latitude was inserted in order to exhibit any striking variations in the dimen- 

 sions of the light at different longitudes. The variations which appear in it, 



however, are not large enough to allow any safe inference from them, unless we 

 could correct them like the latitudes, which seems to be impracticable. They 

 have some relation to the changes in the difference of absorption at the boun- 

 daries, but this would naturally result from the manner in which the difference 

 of absorption was determined. When the light was observed to be wide, the 

 computed difference of absorption is of course larger than when the observed 

 light, under similar circumstances, was relatively narrow. On comparing the 

 observed width with the corresponding results for the inclination of the ecliptic 

 to the horizon, no systematic variation was detected. It seems probable that the 

 width of the light, as observed by Jones, was subject to considerable variation on 

 account of the meteorological conditions prevailing at the time of observation. 

 As the observations were made in various climates and at all seasons of the 

 year, there is little reason to expect from them the discovery of any systematic 

 variation in the width of the light, dependent either upon its zenith distance or 

 upon its longitude. 



Besides the longitudes of the ascending nodes, the other elements determining 

 the form and position of the orbits of asteroids were discussed, but without many 

 results here requiring notice. The inclinations do not appear to depend upon 

 the longitudes of the nodes, the relative proportions of small and large inclina- 

 tions not showing any marked changes at different longitudes. In all, the number 

 of inclinations less than 5° is 78 ; between 5° and 10°, 86 ; between 10° and 15°, 

 45; greater than 15°, 28. We may probably infer that the band formed by the 

 collective orbits would approach the latitude of 10°, north and south, with little 

 diminution of brightness, and would afterwards become fainter rather rapidly. But 

 it should be remembered that asteroids with large inclinations are less likely than 

 others to be discovered. 



The longitudes of the perihelia, using that term in the customary sense, show 

 a tendency to accumulate near the vernal equinox. Between 300° and 60° there 

 are 122 perihelia, while in the remaining 240° of longitude there are only 11-5. 

 It is not easy to explain this peculiarity by the circumstances under w T hich aste- 

 roids have been found. If it indicates a real inequality, the band formed by the 

 collective orbits should on the whole be relatively bright, and, in opposition, rela- 





