264 



Mr. Walker referred to some of the analytical conclusions drawn by Mr. 

 Erman* from the fact, which the Philadelphia observations of this year go to 

 confirm, that these meteors appear to converge nearly to a common point in 

 the heavens. 



" 1st. Mr. Erman concludes, that these bodies are of a cosmical origin ; that 

 they move in a continuous ring-formed stream of not less that 3° in breadth ; 

 that the plane of the centre of this stream is inclined at least 56°, probably 

 more than 90°, and not exceeding 124° to the plane of the ecliptic, — an incli- 

 nation which hitherto comets alone have been known to possess. 



"■ 2d. That their least velocity in space Aug. 10.5th, is 55 hundredths that of 

 the earth in its orbit, giving them a period round the sun of 128 days ; that 

 their greatest velocity is 143 hundredths that of the earth, which would locate 

 them at this time on the perihelion of a parabola or ellipse of period indefi- 

 nitely great. 



" 3d. That to remove this uncertainty of their velocities, between 55 and 

 143 hundredths that of the earth, it is only necessary that two observers, at a 

 distance apart, should trace with precision the apparent path of the same me- 

 teor, and one of them at least its duration. This condition had not yet been 

 fulfilled in Europe, otherwise the entire elements of their orbit would have 

 been approximately determined. 



" 4th. That their perihelion distances are not less than 2 hundredths nor 

 more than 97 hundredths of the earth's mean distance from the sun. 



" 5th. That they are in their descending node when visible Aug. 10.5th, 

 and that their distance from the sun, in the ascending node, is not less than 

 7 hundredths, and may be several times the earth's mean distance from the 

 sun. Hence, even if they are a continuous ellipse-formed stream, it is only in 

 one of these possible distances, viz. that of the earth from the sun ; that this 

 stream would be visible to a spectator on the earth, when traversing its ascend- 

 ing node. If, near the sun, their aggregate might appear as spots on the solar 

 disc, or might intercept some of the solar light and heat: if far beyond the 

 earth, no traces of them would be found. 



- " 6th. That the earth traverses this meteor-stream from the 5.5th to the 

 7.5th of February. The fact that no such stream has of late years been 

 noticed, shows that the first condition of No. 5, does not prevail. Mr. Erman 

 thinks that the diminution of the normal increase of temperature at this date, 

 as ascertained at several stations, for many years past, by Mr. Madler, of Ber- 

 lin, may possibly warrant the conclusion, that the second condition takes 

 place, and that the meteor-stream at this time is between the earth and sun. 

 That the first condition may have prevailed in 1206, and the second in 1208, 

 seems not improbable from history. This apparent change in the appearance 

 of the meteor-stream Mr. Erman ascribes to the secular variations of its ele- 

 ments; the possibility of which is admitted by Olbers and Bessel. 



"7th. That the greatest possible apparent motion of the common point of 

 convergence of their apparent paths, consistent with the existence and ob- 

 served position of this point, is one-tenth of a degree of a great circle west- 

 ward, in an hour." 



* Astr. Nachr., Nos. 385, 390 and 404. 



