114 RESEARCHES CONCERNING THE PERIODICAL 



but we see a constant tendency to condensation into nebulae of particular 

 shapes and degrees of density — into the milky way — into clusters more or less 

 resolvable — into rings, round, or perspectively, or really flattened — into plane- 

 tary discs, which, when turned edgewise towards us, might present, as is often 

 found to be the case, a section of a lens. Now that which is seen in the im- 

 mensity of space, with bodies concerning whose dimensions no conjecture can 

 be formed, may also occur in miniature, with respect to groups of these small 

 asteroids, either from common circumstances connected with their original 

 projectile motion, or origin, or time and place of first falling within the sun's 

 sphere of activity, owing to the sun's proper motion in space. Or, in case of 

 a uniform distribution at any time in a particular portion of the system, their 

 mutual attractions, and those of the other bodies of the system, together with 

 physical changes from variations of temperature, may naturally tend to pro- 

 duce the gradual formation of clusters, or, possibly, of circular or flattened 

 rings or lenses, either continuous or interrupted, the individuals of which 

 continue to circulate round the sun for many years almost in the same planes. 

 A single flock or cluster of these bodies might extend for many thousand, or, 

 possibly, hundred thousand miles, and have a general resemblance, though not 

 a perfect uniformity of their elliptic elements. I have mentioned a general re- 

 semblance in their elements. This is all that could be expected, for a perfect 

 uniformity of elements would require the several bodies of the group to be 

 bound together by some law of fixedness of relative position, like the single 

 particles of a solid, which does not here prevail. 



The principal points in this theory for which I have endeavoured to find 

 known analogies are, 



1. That the perihelia of the orbits of these meteors are gradually aggregated 

 too-ether as the distance from the sun diminishes. 



2. That by far the greater part of these bodies never reach the earth's mean 

 distance. 



3. That while this general law of distribution prevails in the planetary space, 

 portions of this space have, besides the average number conformable to this 

 law, special clusters, groups, or flocks of great extent, possibly composing en- 

 tire rings or lenses embracing the sun. 



4. That the individuals composing these clusters have similar elements of 

 elliptic motion, and continue to move round the sun in a plane which, for a 

 considerable period, undergoes but little change in space. 



