402 Miscellanies. 
whose perihelion distances, respectively, correspond nearly with those 
of Venus and the Earth. It is only necessary to suppose that in some 
planes these bodies exhibit a greater tendency to the formation of clus- 
ters, or possibly of flattened rings, in order to account for anniversary 
periods of remarkable showers ; since the earth revisiting the same plane 
at the same season of the year, and at the same distance from the sun, 
may or may not encounter one of these clusters or parts of a flattened 
ring. But these clusters continuing to moye in the same plane, the earth 
must, if it meet them at all, do so at anniversary periods. On the sup- 
position of a flattened ring, the mode having the same radius vector as 
the earth, these displays might o¢cur for several anniversaries, and then 
cease for an indefinite period, owing to the motion of the apsides of the 
ring ; till the anomaly which has a radius vector equal to the earth’s 
mean distance, again coincides with one of the nodes of the ring. Hence 
the connexion between the periods of the second table, as far as regards 
our knowledge of them is accidental, since they depend not on the or- 
bital period of these bodies round the sun, but on the circumstance of 
the earth’s encountering one of these clusters, or planes abounding in 
them, which is regyjated by a law of distribution of these bodies in plan- 
etary space, that must always remain unknown, for want of data for its 
determinatton. | 
The author conjectures that the meteors termed sporadic, by Quetelet; 
which have no common convergent point, may have their perihelia su- 
perior to those of the periodical meteors, and their aphelia far superior 
to that of the earth. In such a case, their orbital velocity would be as 
great as that of the earth, or greater; and as they move in all varie- 
ties of direction, the earth’s tangential motion does not cause them to 
tend, relatively towards a convergent point, in nearly an opposite direc- 
tion, as it does with meteors moving very slowly in their orbits, whatever 
may be their true directions in space. 
A brief history of the opinions and theories of writers on this sub- 
ject is given; and an oversight pointed out in Prof, Erman’s. paper, 
quoted by the author in an oral communication of August 2ist, 1840. 
This relates to Prof. Erman’s minimum relative velocity of the meteors, 
which, instead of being 0.83, of that of the earth, may be indefinitely 
small, and therefore in his formule [Artronomische Nachrichten, No. 
— a ew give a motion of the convergent point cir great. 
den ntidiasaeieatl ame ee | lS f this 2 peat 
at two different dates on he: ee sie 10th of yest last—Pro- 
ceedings of the American Philosophical Society, Feb. 1841. 
* 
