152 THE APPARENT POSITION OF THE ZODIACAL LIGHT. 



in different quadrants, although its width might vary. The two maxima and 

 minima may probably be explained by the consideration that discoveries of aste- 

 roids are usually made near opposition, and are mpre likely to be made near a 

 node than elsewhere. Such discoveries, with unimportant exceptions, have hith- 

 erto been made in Europe or in the United States, where the weather and the 

 position of the ecliptic in the visible hemisphere make the winter and summer 

 months less favorable than the spring and autumn to the seai-ch for new j^lanets. 

 In Chambers's Astronomy, edition of 1877, the dates of discovery of the first 

 169 asteroids are given : 51 occur in March, April, and May ; 35 in June, July, 

 and August; 62 in September, October, and November; and 21 in December, 

 January, and February. Hence the asteroids most likely to be discovered have 

 hitherto been those having nodes in the parts of the ecliptic which come into 

 opposition in autumn and spring. 



But since a planet may apparently be discovered as readily near one of its 

 nodes as near the other, the peculiar distribution of the nodes of the orbits with 

 southern perihelia cannot easily be explained by the circumstances under which 

 the discoveries have been made. There is, however, no very strong reason to 

 think that it indicates any systematic peculiarity in the orbits of asteroids in 

 general ; for we see that the reversal of the nodes of only thirteen orbits would 

 be enough to eliminate it from the statement just given of the number of ascend- 

 ing nodes in different quadrants. StUl, this number, thirteen, is about one eigh- 

 teenth of the total number of orbits under discussion, so that it is not relatively 

 insignificant, although it is evident that the discovery of a much larger number 

 of small planets than are now known will be desirable for determining the ques- 

 tion whether there is any marked irregularity in the distribution of the nodes of 

 such objects in general. 



K we assume that the distribution of the nodes, in the case of meteoric par- 

 ticles at about the distance of asteroids, is correctly indicated by the asteroids 

 already known, it follows that the zodiacal band formed by their collective orbits 

 would show a tendency to north latitude at the longitude 180°, and to south lati- 

 tude at 0°; for the deficiency of ascending nodes in the quadrant from 220° to 

 310° would occasion a deficiency of extreme north latitudes in the quadrant from 

 310° to 40°, and a similar deficiency of extreme south latitudes in the quadrant 

 from 130° to 220°. Moreover, the tendency to north latitude at 180° would be 

 stronger than that to south latitude at 0° if the entire effect were due to particles 

 having perihelia in south latitude; for, in that case, the deficiency in south lati- 



